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34d26872ed
non-kluge method for controlling the order in which values are fed to an aggregate function. At the same time eliminate the old implementation restriction that DISTINCT was only supported for single-argument aggregates. Possibly release-notable behavioral change: formerly, agg(DISTINCT x) dropped null values of x unconditionally. Now, it does so only if the agg transition function is strict; otherwise nulls are treated as DISTINCT normally would, ie, you get one copy. Andrew Gierth, reviewed by Hitoshi Harada
2324 lines
81 KiB
Plaintext
2324 lines
81 KiB
Plaintext
<!-- $PostgreSQL: pgsql/doc/src/sgml/syntax.sgml,v 1.139 2009/12/15 17:57:46 tgl Exp $ -->
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<chapter id="sql-syntax">
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<title>SQL Syntax</title>
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<indexterm zone="sql-syntax">
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<primary>syntax</primary>
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<secondary>SQL</secondary>
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</indexterm>
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<para>
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This chapter describes the syntax of SQL. It forms the foundation
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for understanding the following chapters which will go into detail
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about how SQL commands are applied to define and modify data.
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</para>
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<para>
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We also advise users who are already familiar with SQL to read this
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chapter carefully because it contains several rules and concepts that
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are implemented inconsistently among SQL databases or that are
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specific to <productname>PostgreSQL</productname>.
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</para>
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<sect1 id="sql-syntax-lexical">
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<title>Lexical Structure</title>
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<indexterm>
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<primary>token</primary>
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</indexterm>
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<para>
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SQL input consists of a sequence of
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<firstterm>commands</firstterm>. A command is composed of a
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sequence of <firstterm>tokens</firstterm>, terminated by a
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semicolon (<quote>;</quote>). The end of the input stream also
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terminates a command. Which tokens are valid depends on the syntax
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of the particular command.
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</para>
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<para>
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A token can be a <firstterm>key word</firstterm>, an
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<firstterm>identifier</firstterm>, a <firstterm>quoted
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identifier</firstterm>, a <firstterm>literal</firstterm> (or
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constant), or a special character symbol. Tokens are normally
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separated by whitespace (space, tab, newline), but need not be if
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there is no ambiguity (which is generally only the case if a
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special character is adjacent to some other token type).
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</para>
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<para>
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Additionally, <firstterm>comments</firstterm> can occur in SQL
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input. They are not tokens, they are effectively equivalent to
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whitespace.
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</para>
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<para>
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For example, the following is (syntactically) valid SQL input:
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<programlisting>
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SELECT * FROM MY_TABLE;
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UPDATE MY_TABLE SET A = 5;
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INSERT INTO MY_TABLE VALUES (3, 'hi there');
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</programlisting>
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This is a sequence of three commands, one per line (although this
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is not required; more than one command can be on a line, and
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commands can usefully be split across lines).
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</para>
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<para>
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The SQL syntax is not very consistent regarding what tokens
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identify commands and which are operands or parameters. The first
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few tokens are generally the command name, so in the above example
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we would usually speak of a <quote>SELECT</quote>, an
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<quote>UPDATE</quote>, and an <quote>INSERT</quote> command. But
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for instance the <command>UPDATE</command> command always requires
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a <token>SET</token> token to appear in a certain position, and
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this particular variation of <command>INSERT</command> also
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requires a <token>VALUES</token> in order to be complete. The
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precise syntax rules for each command are described in <xref linkend="reference">.
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</para>
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<sect2 id="sql-syntax-identifiers">
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<title>Identifiers and Key Words</title>
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<indexterm zone="sql-syntax-identifiers">
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<primary>identifier</primary>
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<secondary>syntax of</secondary>
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</indexterm>
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<indexterm zone="sql-syntax-identifiers">
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<primary>name</primary>
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<secondary>syntax of</secondary>
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</indexterm>
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<indexterm zone="sql-syntax-identifiers">
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<primary>key word</primary>
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<secondary>syntax of</secondary>
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</indexterm>
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<para>
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Tokens such as <token>SELECT</token>, <token>UPDATE</token>, or
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<token>VALUES</token> in the example above are examples of
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<firstterm>key words</firstterm>, that is, words that have a fixed
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meaning in the SQL language. The tokens <token>MY_TABLE</token>
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and <token>A</token> are examples of
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<firstterm>identifiers</firstterm>. They identify names of
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tables, columns, or other database objects, depending on the
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command they are used in. Therefore they are sometimes simply
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called <quote>names</quote>. Key words and identifiers have the
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same lexical structure, meaning that one cannot know whether a
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token is an identifier or a key word without knowing the language.
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A complete list of key words can be found in <xref
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linkend="sql-keywords-appendix">.
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</para>
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<para>
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SQL identifiers and key words must begin with a letter
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(<literal>a</literal>-<literal>z</literal>, but also letters with
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diacritical marks and non-Latin letters) or an underscore
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(<literal>_</literal>). Subsequent characters in an identifier or
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key word can be letters, underscores, digits
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(<literal>0</literal>-<literal>9</literal>), or dollar signs
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(<literal>$</>). Note that dollar signs are not allowed in identifiers
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according to the letter of the SQL standard, so their use might render
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applications less portable.
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The SQL standard will not define a key word that contains
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digits or starts or ends with an underscore, so identifiers of this
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form are safe against possible conflict with future extensions of the
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standard.
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</para>
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<para>
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<indexterm><primary>identifier</primary><secondary>length</secondary></indexterm>
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The system uses no more than <symbol>NAMEDATALEN</symbol>-1
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bytes of an identifier; longer names can be written in
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commands, but they will be truncated. By default,
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<symbol>NAMEDATALEN</symbol> is 64 so the maximum identifier
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length is 63 bytes. If this limit is problematic, it can be raised by
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changing the <symbol>NAMEDATALEN</symbol> constant in
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<filename>src/include/pg_config_manual.h</filename>.
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</para>
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<para>
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<indexterm>
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<primary>case sensitivity</primary>
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<secondary>of SQL commands</secondary>
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</indexterm>
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Identifier and key word names are case insensitive. Therefore:
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<programlisting>
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UPDATE MY_TABLE SET A = 5;
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</programlisting>
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can equivalently be written as:
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<programlisting>
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uPDaTE my_TabLE SeT a = 5;
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</programlisting>
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A convention often used is to write key words in upper
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case and names in lower case, e.g.:
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<programlisting>
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UPDATE my_table SET a = 5;
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</programlisting>
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</para>
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<para>
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<indexterm>
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<primary>quotation marks</primary>
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<secondary>and identifiers</secondary>
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</indexterm>
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There is a second kind of identifier: the <firstterm>delimited
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identifier</firstterm> or <firstterm>quoted
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identifier</firstterm>. It is formed by enclosing an arbitrary
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sequence of characters in double-quotes
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(<literal>"</literal>). <!-- " font-lock mania --> A delimited
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identifier is always an identifier, never a key word. So
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<literal>"select"</literal> could be used to refer to a column or
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table named <quote>select</quote>, whereas an unquoted
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<literal>select</literal> would be taken as a key word and
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would therefore provoke a parse error when used where a table or
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column name is expected. The example can be written with quoted
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identifiers like this:
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<programlisting>
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UPDATE "my_table" SET "a" = 5;
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</programlisting>
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</para>
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<para>
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Quoted identifiers can contain any character, except the character
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with code zero. (To include a double quote, write two double quotes.)
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This allows constructing table or column names that would
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otherwise not be possible, such as ones containing spaces or
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ampersands. The length limitation still applies.
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</para>
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<para>
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<indexterm><primary>Unicode escape</primary><secondary>in
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identifiers</secondary></indexterm> A variant of quoted
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identifiers allows including escaped Unicode characters identified
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by their code points. This variant starts
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with <literal>U&</literal> (upper or lower case U followed by
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ampersand) immediately before the opening double quote, without
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any spaces in between, for example <literal>U&"foo"</literal>.
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(Note that this creates an ambiguity with the
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operator <literal>&</literal>. Use spaces around the operator to
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avoid this problem.) Inside the quotes, Unicode characters can be
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specified in escaped form by writing a backslash followed by the
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four-digit hexadecimal code point number or alternatively a
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backslash followed by a plus sign followed by a six-digit
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hexadecimal code point number. For example, the
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identifier <literal>"data"</literal> could be written as
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<programlisting>
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U&"d\0061t\+000061"
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</programlisting>
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The following less trivial example writes the Russian
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word <quote>slon</quote> (elephant) in Cyrillic letters:
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<programlisting>
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U&"\0441\043B\043E\043D"
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</programlisting>
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</para>
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<para>
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If a different escape character than backslash is desired, it can
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be specified using
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the <literal>UESCAPE</literal><indexterm><primary>UESCAPE</primary></indexterm>
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clause after the string, for example:
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<programlisting>
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U&"d!0061t!+000061" UESCAPE '!'
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</programlisting>
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The escape character can be any single character other than a
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hexadecimal digit, the plus sign, a single quote, a double quote,
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or a whitespace character. Note that the escape character is
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written in single quotes, not double quotes.
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</para>
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<para>
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To include the escape character in the identifier literally, write
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it twice.
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</para>
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<para>
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The Unicode escape syntax works only when the server encoding is
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UTF8. When other server encodings are used, only code points in
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the ASCII range (up to <literal>\007F</literal>) can be specified.
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Both the 4-digit and the 6-digit form can be used to specify
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UTF-16 surrogate pairs to compose characters with code points
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larger than <literal>\FFFF</literal> (although the availability of
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the 6-digit form technically makes this unnecessary).
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</para>
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<para>
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Quoting an identifier also makes it case-sensitive, whereas
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unquoted names are always folded to lower case. For example, the
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identifiers <literal>FOO</literal>, <literal>foo</literal>, and
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<literal>"foo"</literal> are considered the same by
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<productname>PostgreSQL</productname>, but
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<literal>"Foo"</literal> and <literal>"FOO"</literal> are
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different from these three and each other. (The folding of
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unquoted names to lower case in <productname>PostgreSQL</> is
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incompatible with the SQL standard, which says that unquoted names
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should be folded to upper case. Thus, <literal>foo</literal>
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should be equivalent to <literal>"FOO"</literal> not
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<literal>"foo"</literal> according to the standard. If you want
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to write portable applications you are advised to always quote a
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particular name or never quote it.)
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</para>
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</sect2>
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<sect2 id="sql-syntax-constants">
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<title>Constants</title>
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<indexterm zone="sql-syntax-constants">
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<primary>constant</primary>
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</indexterm>
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<para>
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There are three kinds of <firstterm>implicitly-typed
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constants</firstterm> in <productname>PostgreSQL</productname>:
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strings, bit strings, and numbers.
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Constants can also be specified with explicit types, which can
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enable more accurate representation and more efficient handling by
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the system. These alternatives are discussed in the following
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subsections.
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</para>
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<sect3 id="sql-syntax-strings">
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<title>String Constants</title>
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<indexterm zone="sql-syntax-strings">
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<primary>character string</primary>
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<secondary>constant</secondary>
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</indexterm>
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<para>
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<indexterm>
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<primary>quotation marks</primary>
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<secondary>escaping</secondary>
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</indexterm>
|
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A string constant in SQL is an arbitrary sequence of characters
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bounded by single quotes (<literal>'</literal>), for example
|
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<literal>'This is a string'</literal>. To include
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a single-quote character within a string constant,
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write two adjacent single quotes, e.g.,
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<literal>'Dianne''s horse'</literal>.
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Note that this is <emphasis>not</> the same as a double-quote
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character (<literal>"</>). <!-- font-lock sanity: " -->
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</para>
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<para>
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Two string constants that are only separated by whitespace
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<emphasis>with at least one newline</emphasis> are concatenated
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and effectively treated as if the string had been written as one
|
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constant. For example:
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<programlisting>
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SELECT 'foo'
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'bar';
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</programlisting>
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is equivalent to:
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<programlisting>
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SELECT 'foobar';
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</programlisting>
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but:
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<programlisting>
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SELECT 'foo' 'bar';
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</programlisting>
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is not valid syntax. (This slightly bizarre behavior is specified
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by <acronym>SQL</acronym>; <productname>PostgreSQL</productname> is
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following the standard.)
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</para>
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</sect3>
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<sect3 id="sql-syntax-strings-escape">
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<title>String Constants with C-Style Escapes</title>
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<indexterm zone="sql-syntax-strings-escape">
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<primary>escape string syntax</primary>
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</indexterm>
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<indexterm zone="sql-syntax-strings-escape">
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<primary>backslash escapes</primary>
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</indexterm>
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<para>
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<productname>PostgreSQL</productname> also accepts <quote>escape</>
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string constants, which are an extension to the SQL standard.
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An escape string constant is specified by writing the letter
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<literal>E</literal> (upper or lower case) just before the opening single
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quote, e.g., <literal>E'foo'</>. (When continuing an escape string
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constant across lines, write <literal>E</> only before the first opening
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quote.)
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Within an escape string, a backslash character (<literal>\</>) begins a
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C-like <firstterm>backslash escape</> sequence, in which the combination
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of backslash and following character(s) represent a special byte
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value, as shown in <xref linkend="sql-backslash-table">.
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</para>
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<table id="sql-backslash-table">
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<title>Backslash Escape Sequences</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Backslash Escape Sequence</>
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<entry>Interpretation</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><literal>\b</literal></entry>
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<entry>backspace</entry>
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</row>
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<row>
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<entry><literal>\f</literal></entry>
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<entry>form feed</entry>
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</row>
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<row>
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<entry><literal>\n</literal></entry>
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<entry>newline</entry>
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</row>
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<row>
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<entry><literal>\r</literal></entry>
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<entry>carriage return</entry>
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</row>
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<row>
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<entry><literal>\t</literal></entry>
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<entry>tab</entry>
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</row>
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<row>
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<entry>
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<literal>\<replaceable>o</replaceable></literal>,
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<literal>\<replaceable>oo</replaceable></literal>,
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<literal>\<replaceable>ooo</replaceable></literal>
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(<replaceable>o</replaceable> = 0 - 7)
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</entry>
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<entry>octal byte value</entry>
|
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</row>
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<row>
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<entry>
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<literal>\x<replaceable>h</replaceable></literal>,
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<literal>\x<replaceable>hh</replaceable></literal>
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(<replaceable>h</replaceable> = 0 - 9, A - F)
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</entry>
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<entry>hexadecimal byte value</entry>
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</row>
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<row>
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<entry>
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<literal>\u<replaceable>xxxx</replaceable></literal>,
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<literal>\U<replaceable>xxxxxxxx</replaceable></literal>
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(<replaceable>x</replaceable> = 0 - 9, A - F)
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</entry>
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<entry>16 or 32-bit hexadecimal Unicode character value</entry>
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</row>
|
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</tbody>
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</tgroup>
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</table>
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|
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<para>
|
|
Any other
|
|
character following a backslash is taken literally. Thus, to
|
|
include a backslash character, write two backslashes (<literal>\\</>).
|
|
Also, a single quote can be included in an escape string by writing
|
|
<literal>\'</literal>, in addition to the normal way of <literal>''</>.
|
|
</para>
|
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|
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<para>
|
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It is your responsibility that the byte sequences you create,
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|
especially when using the octal or hexadecimal escapes, compose
|
|
valid characters in the server character set encoding. When the
|
|
server encoding is UTF-8, then the Unicode escapes or the
|
|
alternative Unicode escape syntax, explained
|
|
in <xref linkend="sql-syntax-strings-uescape">, should be used
|
|
instead. (The alternative would be doing the UTF-8 encoding by
|
|
hand and writing out the bytes, which would be very cumbersome.)
|
|
</para>
|
|
|
|
<para>
|
|
The Unicode escape syntax works fully only when the server
|
|
encoding is UTF-8. When other server encodings are used, only
|
|
code points in the ASCII range (up to <literal>\u007F</>) can be
|
|
specified. Both the 4-digit and the 8-digit form can be used to
|
|
specify UTF-16 surrogate pairs to compose characters with code
|
|
points larger than <literal>\FFFF</literal> (although the
|
|
availability of the 8-digit form technically makes this
|
|
unnecessary).
|
|
</para>
|
|
|
|
<caution>
|
|
<para>
|
|
If the configuration parameter
|
|
<xref linkend="guc-standard-conforming-strings"> is <literal>off</>,
|
|
then <productname>PostgreSQL</productname> recognizes backslash escapes
|
|
in both regular and escape string constants. This is for backward
|
|
compatibility with the historical behavior, where backslash escapes
|
|
were always recognized.
|
|
Although <varname>standard_conforming_strings</> currently defaults to
|
|
<literal>off</>, the default will change to <literal>on</> in a future
|
|
release for improved standards compliance. Applications are therefore
|
|
encouraged to migrate away from using backslash escapes. If you need
|
|
to use a backslash escape to represent a special character, write the
|
|
string constant with an <literal>E</> to be sure it will be handled the same
|
|
way in future releases.
|
|
</para>
|
|
|
|
<para>
|
|
In addition to <varname>standard_conforming_strings</>, the configuration
|
|
parameters <xref linkend="guc-escape-string-warning"> and
|
|
<xref linkend="guc-backslash-quote"> govern treatment of backslashes
|
|
in string constants.
|
|
</para>
|
|
</caution>
|
|
|
|
<para>
|
|
The character with the code zero cannot be in a string constant.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="sql-syntax-strings-uescape">
|
|
<title>String Constants with Unicode Escapes</title>
|
|
|
|
<indexterm zone="sql-syntax-strings-uescape">
|
|
<primary>Unicode escape</primary>
|
|
<secondary>in string constants</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> also supports another type
|
|
of escape syntax for strings that allows specifying arbitrary
|
|
Unicode characters by code point. A Unicode escape string
|
|
constant starts with <literal>U&</literal> (upper or lower case
|
|
letter U followed by ampersand) immediately before the opening
|
|
quote, without any spaces in between, for
|
|
example <literal>U&'foo'</literal>. (Note that this creates an
|
|
ambiguity with the operator <literal>&</literal>. Use spaces
|
|
around the operator to avoid this problem.) Inside the quotes,
|
|
Unicode characters can be specified in escaped form by writing a
|
|
backslash followed by the four-digit hexadecimal code point
|
|
number or alternatively a backslash followed by a plus sign
|
|
followed by a six-digit hexadecimal code point number. For
|
|
example, the string <literal>'data'</literal> could be written as
|
|
<programlisting>
|
|
U&'d\0061t\+000061'
|
|
</programlisting>
|
|
The following less trivial example writes the Russian
|
|
word <quote>slon</quote> (elephant) in Cyrillic letters:
|
|
<programlisting>
|
|
U&'\0441\043B\043E\043D'
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
If a different escape character than backslash is desired, it can
|
|
be specified using
|
|
the <literal>UESCAPE</literal><indexterm><primary>UESCAPE</primary></indexterm>
|
|
clause after the string, for example:
|
|
<programlisting>
|
|
U&'d!0061t!+000061' UESCAPE '!'
|
|
</programlisting>
|
|
The escape character can be any single character other than a
|
|
hexadecimal digit, the plus sign, a single quote, a double quote,
|
|
or a whitespace character.
|
|
</para>
|
|
|
|
<para>
|
|
The Unicode escape syntax works only when the server encoding is
|
|
UTF8. When other server encodings are used, only code points in
|
|
the ASCII range (up to <literal>\007F</literal>) can be
|
|
specified.
|
|
Both the 4-digit and the 6-digit form can be used to specify
|
|
UTF-16 surrogate pairs to compose characters with code points
|
|
larger than <literal>\FFFF</literal> (although the availability
|
|
of the 6-digit form technically makes this unnecessary).
|
|
</para>
|
|
|
|
<para>
|
|
Also, the Unicode escape syntax for string constants only works
|
|
when the configuration
|
|
parameter <xref linkend="guc-standard-conforming-strings"> is
|
|
turned on. This is because otherwise this syntax could confuse
|
|
clients that parse the SQL statements to the point that it could
|
|
lead to SQL injections and similar security issues. If the
|
|
parameter is set to off, this syntax will be rejected with an
|
|
error message.
|
|
</para>
|
|
|
|
<para>
|
|
To include the escape character in the string literally, write it
|
|
twice.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="sql-syntax-dollar-quoting">
|
|
<title>Dollar-Quoted String Constants</title>
|
|
|
|
<indexterm>
|
|
<primary>dollar quoting</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
While the standard syntax for specifying string constants is usually
|
|
convenient, it can be difficult to understand when the desired string
|
|
contains many single quotes or backslashes, since each of those must
|
|
be doubled. To allow more readable queries in such situations,
|
|
<productname>PostgreSQL</productname> provides another way, called
|
|
<quote>dollar quoting</quote>, to write string constants.
|
|
A dollar-quoted string constant
|
|
consists of a dollar sign (<literal>$</literal>), an optional
|
|
<quote>tag</quote> of zero or more characters, another dollar
|
|
sign, an arbitrary sequence of characters that makes up the
|
|
string content, a dollar sign, the same tag that began this
|
|
dollar quote, and a dollar sign. For example, here are two
|
|
different ways to specify the string <quote>Dianne's horse</>
|
|
using dollar quoting:
|
|
<programlisting>
|
|
$$Dianne's horse$$
|
|
$SomeTag$Dianne's horse$SomeTag$
|
|
</programlisting>
|
|
Notice that inside the dollar-quoted string, single quotes can be
|
|
used without needing to be escaped. Indeed, no characters inside
|
|
a dollar-quoted string are ever escaped: the string content is always
|
|
written literally. Backslashes are not special, and neither are
|
|
dollar signs, unless they are part of a sequence matching the opening
|
|
tag.
|
|
</para>
|
|
|
|
<para>
|
|
It is possible to nest dollar-quoted string constants by choosing
|
|
different tags at each nesting level. This is most commonly used in
|
|
writing function definitions. For example:
|
|
<programlisting>
|
|
$function$
|
|
BEGIN
|
|
RETURN ($1 ~ $q$[\t\r\n\v\\]$q$);
|
|
END;
|
|
$function$
|
|
</programlisting>
|
|
Here, the sequence <literal>$q$[\t\r\n\v\\]$q$</> represents a
|
|
dollar-quoted literal string <literal>[\t\r\n\v\\]</>, which will
|
|
be recognized when the function body is executed by
|
|
<productname>PostgreSQL</>. But since the sequence does not match
|
|
the outer dollar quoting delimiter <literal>$function$</>, it is
|
|
just some more characters within the constant so far as the outer
|
|
string is concerned.
|
|
</para>
|
|
|
|
<para>
|
|
The tag, if any, of a dollar-quoted string follows the same rules
|
|
as an unquoted identifier, except that it cannot contain a dollar sign.
|
|
Tags are case sensitive, so <literal>$tag$String content$tag$</literal>
|
|
is correct, but <literal>$TAG$String content$tag$</literal> is not.
|
|
</para>
|
|
|
|
<para>
|
|
A dollar-quoted string that follows a keyword or identifier must
|
|
be separated from it by whitespace; otherwise the dollar quoting
|
|
delimiter would be taken as part of the preceding identifier.
|
|
</para>
|
|
|
|
<para>
|
|
Dollar quoting is not part of the SQL standard, but it is often a more
|
|
convenient way to write complicated string literals than the
|
|
standard-compliant single quote syntax. It is particularly useful when
|
|
representing string constants inside other constants, as is often needed
|
|
in procedural function definitions. With single-quote syntax, each
|
|
backslash in the above example would have to be written as four
|
|
backslashes, which would be reduced to two backslashes in parsing the
|
|
original string constant, and then to one when the inner string constant
|
|
is re-parsed during function execution.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="sql-syntax-bit-strings">
|
|
<title>Bit-String Constants</title>
|
|
|
|
<indexterm zone="sql-syntax-bit-strings">
|
|
<primary>bit string</primary>
|
|
<secondary>constant</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Bit-string constants look like regular string constants with a
|
|
<literal>B</literal> (upper or lower case) immediately before the
|
|
opening quote (no intervening whitespace), e.g.,
|
|
<literal>B'1001'</literal>. The only characters allowed within
|
|
bit-string constants are <literal>0</literal> and
|
|
<literal>1</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Alternatively, bit-string constants can be specified in hexadecimal
|
|
notation, using a leading <literal>X</literal> (upper or lower case),
|
|
e.g., <literal>X'1FF'</literal>. This notation is equivalent to
|
|
a bit-string constant with four binary digits for each hexadecimal digit.
|
|
</para>
|
|
|
|
<para>
|
|
Both forms of bit-string constant can be continued
|
|
across lines in the same way as regular string constants.
|
|
Dollar quoting cannot be used in a bit-string constant.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3>
|
|
<title>Numeric Constants</title>
|
|
|
|
<indexterm>
|
|
<primary>number</primary>
|
|
<secondary>constant</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Numeric constants are accepted in these general forms:
|
|
<synopsis>
|
|
<replaceable>digits</replaceable>
|
|
<replaceable>digits</replaceable>.<optional><replaceable>digits</replaceable></optional><optional>e<optional>+-</optional><replaceable>digits</replaceable></optional>
|
|
<optional><replaceable>digits</replaceable></optional>.<replaceable>digits</replaceable><optional>e<optional>+-</optional><replaceable>digits</replaceable></optional>
|
|
<replaceable>digits</replaceable>e<optional>+-</optional><replaceable>digits</replaceable>
|
|
</synopsis>
|
|
where <replaceable>digits</replaceable> is one or more decimal
|
|
digits (0 through 9). At least one digit must be before or after the
|
|
decimal point, if one is used. At least one digit must follow the
|
|
exponent marker (<literal>e</literal>), if one is present.
|
|
There cannot be any spaces or other characters embedded in the
|
|
constant. Note that any leading plus or minus sign is not actually
|
|
considered part of the constant; it is an operator applied to the
|
|
constant.
|
|
</para>
|
|
|
|
<para>
|
|
These are some examples of valid numeric constants:
|
|
<literallayout>
|
|
42
|
|
3.5
|
|
4.
|
|
.001
|
|
5e2
|
|
1.925e-3
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
<indexterm><primary>integer</primary></indexterm>
|
|
<indexterm><primary>bigint</primary></indexterm>
|
|
<indexterm><primary>numeric</primary></indexterm>
|
|
A numeric constant that contains neither a decimal point nor an
|
|
exponent is initially presumed to be type <type>integer</> if its
|
|
value fits in type <type>integer</> (32 bits); otherwise it is
|
|
presumed to be type <type>bigint</> if its
|
|
value fits in type <type>bigint</> (64 bits); otherwise it is
|
|
taken to be type <type>numeric</>. Constants that contain decimal
|
|
points and/or exponents are always initially presumed to be type
|
|
<type>numeric</>.
|
|
</para>
|
|
|
|
<para>
|
|
The initially assigned data type of a numeric constant is just a
|
|
starting point for the type resolution algorithms. In most cases
|
|
the constant will be automatically coerced to the most
|
|
appropriate type depending on context. When necessary, you can
|
|
force a numeric value to be interpreted as a specific data type
|
|
by casting it.<indexterm><primary>type cast</primary></indexterm>
|
|
For example, you can force a numeric value to be treated as type
|
|
<type>real</> (<type>float4</>) by writing:
|
|
|
|
<programlisting>
|
|
REAL '1.23' -- string style
|
|
1.23::REAL -- PostgreSQL (historical) style
|
|
</programlisting>
|
|
|
|
These are actually just special cases of the general casting
|
|
notations discussed next.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="sql-syntax-constants-generic">
|
|
<title>Constants of Other Types</title>
|
|
|
|
<indexterm>
|
|
<primary>data type</primary>
|
|
<secondary>constant</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A constant of an <emphasis>arbitrary</emphasis> type can be
|
|
entered using any one of the following notations:
|
|
<synopsis>
|
|
<replaceable>type</replaceable> '<replaceable>string</replaceable>'
|
|
'<replaceable>string</replaceable>'::<replaceable>type</replaceable>
|
|
CAST ( '<replaceable>string</replaceable>' AS <replaceable>type</replaceable> )
|
|
</synopsis>
|
|
The string constant's text is passed to the input conversion
|
|
routine for the type called <replaceable>type</replaceable>. The
|
|
result is a constant of the indicated type. The explicit type
|
|
cast can be omitted if there is no ambiguity as to the type the
|
|
constant must be (for example, when it is assigned directly to a
|
|
table column), in which case it is automatically coerced.
|
|
</para>
|
|
|
|
<para>
|
|
The string constant can be written using either regular SQL
|
|
notation or dollar-quoting.
|
|
</para>
|
|
|
|
<para>
|
|
It is also possible to specify a type coercion using a function-like
|
|
syntax:
|
|
<synopsis>
|
|
<replaceable>typename</replaceable> ( '<replaceable>string</replaceable>' )
|
|
</synopsis>
|
|
but not all type names can be used in this way; see <xref
|
|
linkend="sql-syntax-type-casts"> for details.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>::</literal>, <literal>CAST()</literal>, and
|
|
function-call syntaxes can also be used to specify run-time type
|
|
conversions of arbitrary expressions, as discussed in <xref
|
|
linkend="sql-syntax-type-casts">. To avoid syntactic ambiguity, the
|
|
<literal><replaceable>type</> '<replaceable>string</>'</literal>
|
|
syntax can only be used to specify the type of a simple literal constant.
|
|
Another restriction on the
|
|
<literal><replaceable>type</> '<replaceable>string</>'</literal>
|
|
syntax is that it does not work for array types; use <literal>::</literal>
|
|
or <literal>CAST()</literal> to specify the type of an array constant.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>CAST()</> syntax conforms to SQL. The
|
|
<literal><replaceable>type</> '<replaceable>string</>'</literal>
|
|
syntax is a generalization of the standard: SQL specifies this syntax only
|
|
for a few data types, but <productname>PostgreSQL</productname> allows it
|
|
for all types. The syntax with
|
|
<literal>::</literal> is historical <productname>PostgreSQL</productname>
|
|
usage, as is the function-call syntax.
|
|
</para>
|
|
</sect3>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-operators">
|
|
<title>Operators</title>
|
|
|
|
<indexterm zone="sql-syntax-operators">
|
|
<primary>operator</primary>
|
|
<secondary>syntax</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
An operator name is a sequence of up to <symbol>NAMEDATALEN</symbol>-1
|
|
(63 by default) characters from the following list:
|
|
<literallayout>
|
|
+ - * / < > = ~ ! @ # % ^ & | ` ?
|
|
</literallayout>
|
|
|
|
There are a few restrictions on operator names, however:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
<literal>--</literal> and <literal>/*</literal> cannot appear
|
|
anywhere in an operator name, since they will be taken as the
|
|
start of a comment.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A multiple-character operator name cannot end in <literal>+</> or <literal>-</>,
|
|
unless the name also contains at least one of these characters:
|
|
<literallayout>
|
|
~ ! @ # % ^ & | ` ?
|
|
</literallayout>
|
|
For example, <literal>@-</literal> is an allowed operator name,
|
|
but <literal>*-</literal> is not. This restriction allows
|
|
<productname>PostgreSQL</productname> to parse SQL-compliant
|
|
queries without requiring spaces between tokens.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
When working with non-SQL-standard operator names, you will usually
|
|
need to separate adjacent operators with spaces to avoid ambiguity.
|
|
For example, if you have defined a left unary operator named <literal>@</literal>,
|
|
you cannot write <literal>X*@Y</literal>; you must write
|
|
<literal>X* @Y</literal> to ensure that
|
|
<productname>PostgreSQL</productname> reads it as two operator names
|
|
not one.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Special Characters</title>
|
|
|
|
<para>
|
|
Some characters that are not alphanumeric have a special meaning
|
|
that is different from being an operator. Details on the usage can
|
|
be found at the location where the respective syntax element is
|
|
described. This section only exists to advise the existence and
|
|
summarize the purposes of these characters.
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
A dollar sign (<literal>$</literal>) followed by digits is used
|
|
to represent a positional parameter in the body of a function
|
|
definition or a prepared statement. In other contexts the
|
|
dollar sign can be part of an identifier or a dollar-quoted string
|
|
constant.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Parentheses (<literal>()</literal>) have their usual meaning to
|
|
group expressions and enforce precedence. In some cases
|
|
parentheses are required as part of the fixed syntax of a
|
|
particular SQL command.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Brackets (<literal>[]</literal>) are used to select the elements
|
|
of an array. See <xref linkend="arrays"> for more information
|
|
on arrays.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Commas (<literal>,</literal>) are used in some syntactical
|
|
constructs to separate the elements of a list.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The semicolon (<literal>;</literal>) terminates an SQL command.
|
|
It cannot appear anywhere within a command, except within a
|
|
string constant or quoted identifier.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The colon (<literal>:</literal>) is used to select
|
|
<quote>slices</quote> from arrays. (See <xref
|
|
linkend="arrays">.) In certain SQL dialects (such as Embedded
|
|
SQL), the colon is used to prefix variable names.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The asterisk (<literal>*</literal>) is used in some contexts to denote
|
|
all the fields of a table row or composite value. It also
|
|
has a special meaning when used as the argument of an
|
|
aggregate function, namely that the aggregate does not require
|
|
any explicit parameter.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
The period (<literal>.</literal>) is used in numeric
|
|
constants, and to separate schema, table, and column names.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-comments">
|
|
<title>Comments</title>
|
|
|
|
<indexterm zone="sql-syntax-comments">
|
|
<primary>comment</primary>
|
|
<secondary sortas="SQL">in SQL</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A comment is a sequence of characters beginning with
|
|
double dashes and extending to the end of the line, e.g.:
|
|
<programlisting>
|
|
-- This is a standard SQL comment
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Alternatively, C-style block comments can be used:
|
|
<programlisting>
|
|
/* multiline comment
|
|
* with nesting: /* nested block comment */
|
|
*/
|
|
</programlisting>
|
|
where the comment begins with <literal>/*</literal> and extends to
|
|
the matching occurrence of <literal>*/</literal>. These block
|
|
comments nest, as specified in the SQL standard but unlike C, so that one can
|
|
comment out larger blocks of code that might contain existing block
|
|
comments.
|
|
</para>
|
|
|
|
<para>
|
|
A comment is removed from the input stream before further syntax
|
|
analysis and is effectively replaced by whitespace.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-precedence">
|
|
<title>Lexical Precedence</title>
|
|
|
|
<indexterm zone="sql-precedence">
|
|
<primary>operator</primary>
|
|
<secondary>precedence</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
<xref linkend="sql-precedence-table"> shows the precedence and
|
|
associativity of the operators in <productname>PostgreSQL</>.
|
|
Most operators have the same precedence and are left-associative.
|
|
The precedence and associativity of the operators is hard-wired
|
|
into the parser. This can lead to non-intuitive behavior; for
|
|
example the Boolean operators <literal><</> and
|
|
<literal>></> have a different precedence than the Boolean
|
|
operators <literal><=</> and <literal>>=</>. Also, you will
|
|
sometimes need to add parentheses when using combinations of
|
|
binary and unary operators. For instance:
|
|
<programlisting>
|
|
SELECT 5 ! - 6;
|
|
</programlisting>
|
|
will be parsed as:
|
|
<programlisting>
|
|
SELECT 5 ! (- 6);
|
|
</programlisting>
|
|
because the parser has no idea — until it is too late
|
|
— that <token>!</token> is defined as a postfix operator,
|
|
not an infix one. To get the desired behavior in this case, you
|
|
must write:
|
|
<programlisting>
|
|
SELECT (5 !) - 6;
|
|
</programlisting>
|
|
This is the price one pays for extensibility.
|
|
</para>
|
|
|
|
<table id="sql-precedence-table">
|
|
<title>Operator Precedence (decreasing)</title>
|
|
|
|
<tgroup cols="3">
|
|
<thead>
|
|
<row>
|
|
<entry>Operator/Element</entry>
|
|
<entry>Associativity</entry>
|
|
<entry>Description</entry>
|
|
</row>
|
|
</thead>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry><token>.</token></entry>
|
|
<entry>left</entry>
|
|
<entry>table/column name separator</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>::</token></entry>
|
|
<entry>left</entry>
|
|
<entry><productname>PostgreSQL</productname>-style typecast</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>[</token> <token>]</token></entry>
|
|
<entry>left</entry>
|
|
<entry>array element selection</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>-</token></entry>
|
|
<entry>right</entry>
|
|
<entry>unary minus</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>^</token></entry>
|
|
<entry>left</entry>
|
|
<entry>exponentiation</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>*</token> <token>/</token> <token>%</token></entry>
|
|
<entry>left</entry>
|
|
<entry>multiplication, division, modulo</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>+</token> <token>-</token></entry>
|
|
<entry>left</entry>
|
|
<entry>addition, subtraction</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>IS</token></entry>
|
|
<entry></entry>
|
|
<entry><literal>IS TRUE</>, <literal>IS FALSE</>, <literal>IS UNKNOWN</>, <literal>IS NULL</></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>ISNULL</token></entry>
|
|
<entry></entry>
|
|
<entry>test for null</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>NOTNULL</token></entry>
|
|
<entry></entry>
|
|
<entry>test for not null</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>(any other)</entry>
|
|
<entry>left</entry>
|
|
<entry>all other native and user-defined operators</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>IN</token></entry>
|
|
<entry></entry>
|
|
<entry>set membership</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>BETWEEN</token></entry>
|
|
<entry></entry>
|
|
<entry>range containment</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>OVERLAPS</token></entry>
|
|
<entry></entry>
|
|
<entry>time interval overlap</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>LIKE</token> <token>ILIKE</token> <token>SIMILAR</token></entry>
|
|
<entry></entry>
|
|
<entry>string pattern matching</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token><</token> <token>></token></entry>
|
|
<entry></entry>
|
|
<entry>less than, greater than</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>=</token></entry>
|
|
<entry>right</entry>
|
|
<entry>equality, assignment</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>NOT</token></entry>
|
|
<entry>right</entry>
|
|
<entry>logical negation</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>AND</token></entry>
|
|
<entry>left</entry>
|
|
<entry>logical conjunction</entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><token>OR</token></entry>
|
|
<entry>left</entry>
|
|
<entry>logical disjunction</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>
|
|
Note that the operator precedence rules also apply to user-defined
|
|
operators that have the same names as the built-in operators
|
|
mentioned above. For example, if you define a
|
|
<quote>+</quote> operator for some custom data type it will have
|
|
the same precedence as the built-in <quote>+</quote> operator, no
|
|
matter what yours does.
|
|
</para>
|
|
|
|
<para>
|
|
When a schema-qualified operator name is used in the
|
|
<literal>OPERATOR</> syntax, as for example in:
|
|
<programlisting>
|
|
SELECT 3 OPERATOR(pg_catalog.+) 4;
|
|
</programlisting>
|
|
the <literal>OPERATOR</> construct is taken to have the default precedence
|
|
shown in <xref linkend="sql-precedence-table"> for <quote>any other</> operator. This is true no matter
|
|
which specific operator appears inside <literal>OPERATOR()</>.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="sql-expressions">
|
|
<title>Value Expressions</title>
|
|
|
|
<indexterm zone="sql-expressions">
|
|
<primary>expression</primary>
|
|
<secondary>syntax</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm zone="sql-expressions">
|
|
<primary>value expression</primary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>scalar</primary>
|
|
<see>expression</see>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Value expressions are used in a variety of contexts, such
|
|
as in the target list of the <command>SELECT</command> command, as
|
|
new column values in <command>INSERT</command> or
|
|
<command>UPDATE</command>, or in search conditions in a number of
|
|
commands. The result of a value expression is sometimes called a
|
|
<firstterm>scalar</firstterm>, to distinguish it from the result of
|
|
a table expression (which is a table). Value expressions are
|
|
therefore also called <firstterm>scalar expressions</firstterm> (or
|
|
even simply <firstterm>expressions</firstterm>). The expression
|
|
syntax allows the calculation of values from primitive parts using
|
|
arithmetic, logical, set, and other operations.
|
|
</para>
|
|
|
|
<para>
|
|
A value expression is one of the following:
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
A constant or literal value
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A column reference
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A positional parameter reference, in the body of a function definition
|
|
or prepared statement
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A subscripted expression
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A field selection expression
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
An operator invocation
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A function call
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
An aggregate expression
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A window function call
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A type cast
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A scalar subquery
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
An array constructor
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
A row constructor
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Another value expression in parentheses (used to group
|
|
subexpressions and override
|
|
precedence<indexterm><primary>parenthesis</></>)
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
In addition to this list, there are a number of constructs that can
|
|
be classified as an expression but do not follow any general syntax
|
|
rules. These generally have the semantics of a function or
|
|
operator and are explained in the appropriate location in <xref
|
|
linkend="functions">. An example is the <literal>IS NULL</literal>
|
|
clause.
|
|
</para>
|
|
|
|
<para>
|
|
We have already discussed constants in <xref
|
|
linkend="sql-syntax-constants">. The following sections discuss
|
|
the remaining options.
|
|
</para>
|
|
|
|
<sect2>
|
|
<title>Column References</title>
|
|
|
|
<indexterm>
|
|
<primary>column reference</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A column can be referenced in the form:
|
|
<synopsis>
|
|
<replaceable>correlation</replaceable>.<replaceable>columnname</replaceable>
|
|
</synopsis>
|
|
</para>
|
|
|
|
<para>
|
|
<replaceable>correlation</replaceable> is the name of a
|
|
table (possibly qualified with a schema name), or an alias for a table
|
|
defined by means of a <literal>FROM</literal> clause.
|
|
The correlation name and separating dot can be omitted if the column name
|
|
is unique across all the tables being used in the current query. (See also <xref linkend="queries">.)
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Positional Parameters</title>
|
|
|
|
<indexterm>
|
|
<primary>parameter</primary>
|
|
<secondary>syntax</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>$</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A positional parameter reference is used to indicate a value
|
|
that is supplied externally to an SQL statement. Parameters are
|
|
used in SQL function definitions and in prepared queries. Some
|
|
client libraries also support specifying data values separately
|
|
from the SQL command string, in which case parameters are used to
|
|
refer to the out-of-line data values.
|
|
The form of a parameter reference is:
|
|
<synopsis>
|
|
$<replaceable>number</replaceable>
|
|
</synopsis>
|
|
</para>
|
|
|
|
<para>
|
|
For example, consider the definition of a function,
|
|
<function>dept</function>, as:
|
|
|
|
<programlisting>
|
|
CREATE FUNCTION dept(text) RETURNS dept
|
|
AS $$ SELECT * FROM dept WHERE name = $1 $$
|
|
LANGUAGE SQL;
|
|
</programlisting>
|
|
|
|
Here the <literal>$1</literal> references the value of the first
|
|
function argument whenever the function is invoked.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Subscripts</title>
|
|
|
|
<indexterm>
|
|
<primary>subscript</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
If an expression yields a value of an array type, then a specific
|
|
element of the array value can be extracted by writing
|
|
<synopsis>
|
|
<replaceable>expression</replaceable>[<replaceable>subscript</replaceable>]
|
|
</synopsis>
|
|
or multiple adjacent elements (an <quote>array slice</>) can be extracted
|
|
by writing
|
|
<synopsis>
|
|
<replaceable>expression</replaceable>[<replaceable>lower_subscript</replaceable>:<replaceable>upper_subscript</replaceable>]
|
|
</synopsis>
|
|
(Here, the brackets <literal>[ ]</literal> are meant to appear literally.)
|
|
Each <replaceable>subscript</replaceable> is itself an expression,
|
|
which must yield an integer value.
|
|
</para>
|
|
|
|
<para>
|
|
In general the array <replaceable>expression</replaceable> must be
|
|
parenthesized, but the parentheses can be omitted when the expression
|
|
to be subscripted is just a column reference or positional parameter.
|
|
Also, multiple subscripts can be concatenated when the original array
|
|
is multidimensional.
|
|
For example:
|
|
|
|
<programlisting>
|
|
mytable.arraycolumn[4]
|
|
mytable.two_d_column[17][34]
|
|
$1[10:42]
|
|
(arrayfunction(a,b))[42]
|
|
</programlisting>
|
|
|
|
The parentheses in the last example are required.
|
|
See <xref linkend="arrays"> for more about arrays.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Field Selection</title>
|
|
|
|
<indexterm>
|
|
<primary>field selection</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
If an expression yields a value of a composite type (row type), then a
|
|
specific field of the row can be extracted by writing
|
|
<synopsis>
|
|
<replaceable>expression</replaceable>.<replaceable>fieldname</replaceable>
|
|
</synopsis>
|
|
</para>
|
|
|
|
<para>
|
|
In general the row <replaceable>expression</replaceable> must be
|
|
parenthesized, but the parentheses can be omitted when the expression
|
|
to be selected from is just a table reference or positional parameter.
|
|
For example:
|
|
|
|
<programlisting>
|
|
mytable.mycolumn
|
|
$1.somecolumn
|
|
(rowfunction(a,b)).col3
|
|
</programlisting>
|
|
|
|
(Thus, a qualified column reference is actually just a special case
|
|
of the field selection syntax.) An important special case is
|
|
extracting a field from a table column that is of a composite type:
|
|
|
|
<programlisting>
|
|
(compositecol).somefield
|
|
(mytable.compositecol).somefield
|
|
</programlisting>
|
|
|
|
The parentheses are required here to show that
|
|
<structfield>compositecol</> is a column name not a table name,
|
|
or that <structname>mytable</> is a table name not a schema name
|
|
in the second case.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Operator Invocations</title>
|
|
|
|
<indexterm>
|
|
<primary>operator</primary>
|
|
<secondary>invocation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
There are three possible syntaxes for an operator invocation:
|
|
<simplelist>
|
|
<member><replaceable>expression</replaceable> <replaceable>operator</replaceable> <replaceable>expression</replaceable> (binary infix operator)</member>
|
|
<member><replaceable>operator</replaceable> <replaceable>expression</replaceable> (unary prefix operator)</member>
|
|
<member><replaceable>expression</replaceable> <replaceable>operator</replaceable> (unary postfix operator)</member>
|
|
</simplelist>
|
|
where the <replaceable>operator</replaceable> token follows the syntax
|
|
rules of <xref linkend="sql-syntax-operators">, or is one of the
|
|
key words <token>AND</token>, <token>OR</token>, and
|
|
<token>NOT</token>, or is a qualified operator name in the form:
|
|
<synopsis>
|
|
<literal>OPERATOR(</><replaceable>schema</><literal>.</><replaceable>operatorname</><literal>)</>
|
|
</synopsis>
|
|
Which particular operators exist and whether
|
|
they are unary or binary depends on what operators have been
|
|
defined by the system or the user. <xref linkend="functions">
|
|
describes the built-in operators.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Function Calls</title>
|
|
|
|
<indexterm>
|
|
<primary>function</primary>
|
|
<secondary>invocation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
The syntax for a function call is the name of a function
|
|
(possibly qualified with a schema name), followed by its argument list
|
|
enclosed in parentheses:
|
|
|
|
<synopsis>
|
|
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional> )
|
|
</synopsis>
|
|
</para>
|
|
|
|
<para>
|
|
For example, the following computes the square root of 2:
|
|
<programlisting>
|
|
sqrt(2)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
The list of built-in functions is in <xref linkend="functions">.
|
|
Other functions can be added by the user.
|
|
</para>
|
|
|
|
<para>
|
|
The arguments can optionally have names attached.
|
|
See <xref linkend="sql-syntax-calling-funcs"> for details.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="syntax-aggregates">
|
|
<title>Aggregate Expressions</title>
|
|
|
|
<indexterm zone="syntax-aggregates">
|
|
<primary>aggregate function</primary>
|
|
<secondary>invocation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
An <firstterm>aggregate expression</firstterm> represents the
|
|
application of an aggregate function across the rows selected by a
|
|
query. An aggregate function reduces multiple inputs to a single
|
|
output value, such as the sum or average of the inputs. The
|
|
syntax of an aggregate expression is one of the following:
|
|
|
|
<synopsis>
|
|
<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
|
|
<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
|
|
<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
|
|
<replaceable>aggregate_name</replaceable> ( * )
|
|
</synopsis>
|
|
|
|
where <replaceable>aggregate_name</replaceable> is a previously
|
|
defined aggregate (possibly qualified with a schema name),
|
|
<replaceable>expression</replaceable> is
|
|
any value expression that does not itself contain an aggregate
|
|
expression or a window function call, and
|
|
<replaceable>order_by_clause</replaceable> is a optional
|
|
<literal>ORDER BY</> clause as described below.
|
|
</para>
|
|
|
|
<para>
|
|
The first form of aggregate expression invokes the aggregate
|
|
across all input rows for which the given expression(s) yield
|
|
non-null values. (Actually, it is up to the aggregate function
|
|
whether to ignore null values or not — but all the standard ones do.)
|
|
The second form is the same as the first, since
|
|
<literal>ALL</literal> is the default. The third form invokes the
|
|
aggregate for all distinct values of the expressions found
|
|
in the input rows (ignoring nulls if the function chooses to do so).
|
|
The last form invokes the aggregate once for
|
|
each input row regardless of null or non-null values; since no
|
|
particular input value is specified, it is generally only useful
|
|
for the <function>count(*)</function> aggregate function.
|
|
</para>
|
|
|
|
<para>
|
|
For example, <literal>count(*)</literal> yields the total number
|
|
of input rows; <literal>count(f1)</literal> yields the number of
|
|
input rows in which <literal>f1</literal> is non-null;
|
|
<literal>count(distinct f1)</literal> yields the number of
|
|
distinct non-null values of <literal>f1</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Ordinarily, the input rows are fed to the aggregate function in an
|
|
unspecified order. In many cases this does not matter; for example,
|
|
<function>min</> produces the same result no matter what order it
|
|
receives the inputs in. However, some aggregate functions
|
|
(such as <function>array_agg</> and <function>xmlagg</>) produce
|
|
results that depend on the ordering of the input rows. When using
|
|
such an aggregate, the optional <replaceable>order_by_clause</> can be
|
|
used to specify the desired ordering. The <replaceable>order_by_clause</>
|
|
has the same syntax as for a query-level <literal>ORDER BY</> clause, as
|
|
described in <xref linkend="queries-order">, except that its expressions
|
|
are always just expressions and cannot be output-column names or numbers.
|
|
For example:
|
|
|
|
<programlisting>
|
|
SELECT array_agg(a ORDER BY b DESC) FROM table;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
If <literal>DISTINCT</> is specified in addition to an
|
|
<replaceable>order_by_clause</>, then all the <literal>ORDER BY</>
|
|
expressions must match regular arguments of the aggregate; that is,
|
|
you cannot sort on an expression that is not included in the
|
|
<literal>DISTINCT</> list.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
The ability to specify both <literal>DISTINCT</> and <literal>ORDER BY</>
|
|
in an aggregate function is a <productname>PostgreSQL</> extension.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
The predefined aggregate functions are described in <xref
|
|
linkend="functions-aggregate">. Other aggregate functions can be added
|
|
by the user.
|
|
</para>
|
|
|
|
<para>
|
|
An aggregate expression can only appear in the result list or
|
|
<literal>HAVING</> clause of a <command>SELECT</> command.
|
|
It is forbidden in other clauses, such as <literal>WHERE</>,
|
|
because those clauses are logically evaluated before the results
|
|
of aggregates are formed.
|
|
</para>
|
|
|
|
<para>
|
|
When an aggregate expression appears in a subquery (see
|
|
<xref linkend="sql-syntax-scalar-subqueries"> and
|
|
<xref linkend="functions-subquery">), the aggregate is normally
|
|
evaluated over the rows of the subquery. But an exception occurs
|
|
if the aggregate's arguments contain only outer-level variables:
|
|
the aggregate then belongs to the nearest such outer level, and is
|
|
evaluated over the rows of that query. The aggregate expression
|
|
as a whole is then an outer reference for the subquery it appears in,
|
|
and acts as a constant over any one evaluation of that subquery.
|
|
The restriction about
|
|
appearing only in the result list or <literal>HAVING</> clause
|
|
applies with respect to the query level that the aggregate belongs to.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="syntax-window-functions">
|
|
<title>Window Function Calls</title>
|
|
|
|
<indexterm zone="syntax-window-functions">
|
|
<primary>window function</primary>
|
|
<secondary>invocation</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm zone="syntax-window-functions">
|
|
<primary>OVER clause</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A <firstterm>window function call</firstterm> represents the application
|
|
of an aggregate-like function over some portion of the rows selected
|
|
by a query. Unlike regular aggregate function calls, this is not tied
|
|
to grouping of the selected rows into a single output row — each
|
|
row remains separate in the query output. However the window function
|
|
is able to scan all the rows that would be part of the current row's
|
|
group according to the grouping specification (<literal>PARTITION BY</>
|
|
list) of the window function call.
|
|
The syntax of a window function call is one of the following:
|
|
|
|
<synopsis>
|
|
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER ( <replaceable class="parameter">window_definition</replaceable> )
|
|
<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER <replaceable>window_name</replaceable>
|
|
<replaceable>function_name</replaceable> ( * ) OVER ( <replaceable class="parameter">window_definition</replaceable> )
|
|
<replaceable>function_name</replaceable> ( * ) OVER <replaceable>window_name</replaceable>
|
|
</synopsis>
|
|
where <replaceable class="parameter">window_definition</replaceable>
|
|
has the syntax
|
|
<synopsis>
|
|
[ <replaceable class="parameter">existing_window_name</replaceable> ]
|
|
[ PARTITION BY <replaceable class="parameter">expression</replaceable> [, ...] ]
|
|
[ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC | USING <replaceable class="parameter">operator</replaceable> ] [ NULLS { FIRST | LAST } ] [, ...] ]
|
|
[ <replaceable class="parameter">frame_clause</replaceable> ]
|
|
</synopsis>
|
|
and the optional <replaceable class="parameter">frame_clause</replaceable>
|
|
can be one of
|
|
<synopsis>
|
|
RANGE UNBOUNDED PRECEDING
|
|
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
|
|
RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
|
|
ROWS UNBOUNDED PRECEDING
|
|
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
|
|
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
|
|
</synopsis>
|
|
|
|
Here, <replaceable>expression</replaceable> represents any value
|
|
expression that does not itself contain window function calls.
|
|
The <literal>PARTITION BY</> and <literal>ORDER BY</> lists have
|
|
essentially the same syntax and semantics as <literal>GROUP BY</>
|
|
and <literal>ORDER BY</> clauses of the whole query, except that their
|
|
expressions are always just expressions and cannot be output-column
|
|
names or numbers.
|
|
<replaceable>window_name</replaceable> is a reference to a named window
|
|
specification defined in the query's <literal>WINDOW</literal> clause.
|
|
Named window specifications are usually referenced with just
|
|
<literal>OVER</> <replaceable>window_name</replaceable>, but it is
|
|
also possible to write a window name inside the parentheses and then
|
|
optionally supply an ordering clause and/or frame clause (the referenced
|
|
window must lack these clauses, if they are supplied here).
|
|
This latter syntax follows the same rules as modifying an existing
|
|
window name within the <literal>WINDOW</literal> clause; see the
|
|
<xref linkend="sql-select" endterm="sql-select-title"> reference
|
|
page for details.
|
|
</para>
|
|
|
|
<para>
|
|
The <replaceable class="parameter">frame_clause</replaceable> specifies
|
|
the set of rows constituting the <firstterm>window frame</>, for those
|
|
window functions that act on the frame instead of the whole partition.
|
|
The default framing option is <literal>RANGE UNBOUNDED PRECEDING</>,
|
|
which is the same as <literal>RANGE BETWEEN UNBOUNDED PRECEDING AND
|
|
CURRENT ROW</>; it selects rows up through the current row's last
|
|
peer in the <literal>ORDER BY</> ordering (which means all rows if
|
|
there is no <literal>ORDER BY</>). The options
|
|
<literal>RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</> and
|
|
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING</>
|
|
are also equivalent: they always select all rows in the partition.
|
|
Lastly, <literal>ROWS UNBOUNDED PRECEDING</> or its verbose equivalent
|
|
<literal>ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</> select
|
|
all rows up through the current row (regardless of duplicates).
|
|
Beware that this option can produce implementation-dependent results
|
|
if the <literal>ORDER BY</> ordering does not order the rows uniquely.
|
|
</para>
|
|
|
|
<para>
|
|
The built-in window functions are described in <xref
|
|
linkend="functions-window-table">. Other window functions can be added by
|
|
the user. Also, any built-in or user-defined aggregate function can be
|
|
used as a window function.
|
|
</para>
|
|
|
|
<para>
|
|
The syntaxes using <literal>*</> are used for calling parameter-less
|
|
aggregate functions as window functions, for example
|
|
<literal>count(*) OVER (PARTITION BY x ORDER BY y)</>.
|
|
<literal>*</> is customarily not used for non-aggregate window functions.
|
|
Aggregate window functions, unlike normal aggregate functions, do not
|
|
allow <literal>DISTINCT</> or <literal>ORDER BY</> to be used within the
|
|
function argument list.
|
|
</para>
|
|
|
|
<para>
|
|
Window function calls are permitted only in the <literal>SELECT</literal>
|
|
list and the <literal>ORDER BY</> clause of the query.
|
|
</para>
|
|
|
|
<para>
|
|
More information about window functions can be found in
|
|
<xref linkend="tutorial-window"> and
|
|
<xref linkend="queries-window">.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-type-casts">
|
|
<title>Type Casts</title>
|
|
|
|
<indexterm>
|
|
<primary>data type</primary>
|
|
<secondary>type cast</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>type cast</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A type cast specifies a conversion from one data type to another.
|
|
<productname>PostgreSQL</productname> accepts two equivalent syntaxes
|
|
for type casts:
|
|
<synopsis>
|
|
CAST ( <replaceable>expression</replaceable> AS <replaceable>type</replaceable> )
|
|
<replaceable>expression</replaceable>::<replaceable>type</replaceable>
|
|
</synopsis>
|
|
The <literal>CAST</> syntax conforms to SQL; the syntax with
|
|
<literal>::</literal> is historical <productname>PostgreSQL</productname>
|
|
usage.
|
|
</para>
|
|
|
|
<para>
|
|
When a cast is applied to a value expression of a known type, it
|
|
represents a run-time type conversion. The cast will succeed only
|
|
if a suitable type conversion operation has been defined. Notice that this
|
|
is subtly different from the use of casts with constants, as shown in
|
|
<xref linkend="sql-syntax-constants-generic">. A cast applied to an
|
|
unadorned string literal represents the initial assignment of a type
|
|
to a literal constant value, and so it will succeed for any type
|
|
(if the contents of the string literal are acceptable input syntax for the
|
|
data type).
|
|
</para>
|
|
|
|
<para>
|
|
An explicit type cast can usually be omitted if there is no ambiguity as
|
|
to the type that a value expression must produce (for example, when it is
|
|
assigned to a table column); the system will automatically apply a
|
|
type cast in such cases. However, automatic casting is only done for
|
|
casts that are marked <quote>OK to apply implicitly</>
|
|
in the system catalogs. Other casts must be invoked with
|
|
explicit casting syntax. This restriction is intended to prevent
|
|
surprising conversions from being applied silently.
|
|
</para>
|
|
|
|
<para>
|
|
It is also possible to specify a type cast using a function-like
|
|
syntax:
|
|
<synopsis>
|
|
<replaceable>typename</replaceable> ( <replaceable>expression</replaceable> )
|
|
</synopsis>
|
|
However, this only works for types whose names are also valid as
|
|
function names. For example, <literal>double precision</literal>
|
|
cannot be used this way, but the equivalent <literal>float8</literal>
|
|
can. Also, the names <literal>interval</>, <literal>time</>, and
|
|
<literal>timestamp</> can only be used in this fashion if they are
|
|
double-quoted, because of syntactic conflicts. Therefore, the use of
|
|
the function-like cast syntax leads to inconsistencies and should
|
|
probably be avoided.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
The function-like syntax is in fact just a function call. When
|
|
one of the two standard cast syntaxes is used to do a run-time
|
|
conversion, it will internally invoke a registered function to
|
|
perform the conversion. By convention, these conversion functions
|
|
have the same name as their output type, and thus the <quote>function-like
|
|
syntax</> is nothing more than a direct invocation of the underlying
|
|
conversion function. Obviously, this is not something that a portable
|
|
application should rely on. For further details see
|
|
<xref linkend="sql-createcast" endterm="sql-createcast-title">.
|
|
</para>
|
|
</note>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-scalar-subqueries">
|
|
<title>Scalar Subqueries</title>
|
|
|
|
<indexterm>
|
|
<primary>subquery</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A scalar subquery is an ordinary
|
|
<command>SELECT</command> query in parentheses that returns exactly one
|
|
row with one column. (See <xref linkend="queries"> for information about writing queries.)
|
|
The <command>SELECT</command> query is executed
|
|
and the single returned value is used in the surrounding value expression.
|
|
It is an error to use a query that
|
|
returns more than one row or more than one column as a scalar subquery.
|
|
(But if, during a particular execution, the subquery returns no rows,
|
|
there is no error; the scalar result is taken to be null.)
|
|
The subquery can refer to variables from the surrounding query,
|
|
which will act as constants during any one evaluation of the subquery.
|
|
See also <xref linkend="functions-subquery"> for other expressions involving subqueries.
|
|
</para>
|
|
|
|
<para>
|
|
For example, the following finds the largest city population in each
|
|
state:
|
|
<programlisting>
|
|
SELECT name, (SELECT max(pop) FROM cities WHERE cities.state = states.name)
|
|
FROM states;
|
|
</programlisting>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-array-constructors">
|
|
<title>Array Constructors</title>
|
|
|
|
<indexterm>
|
|
<primary>array</primary>
|
|
<secondary>constructor</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>ARRAY</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
An array constructor is an expression that builds an
|
|
array value using values for its member elements. A simple array
|
|
constructor
|
|
consists of the key word <literal>ARRAY</literal>, a left square bracket
|
|
<literal>[</>, a list of expressions (separated by commas) for the
|
|
array element values, and finally a right square bracket <literal>]</>.
|
|
For example:
|
|
<programlisting>
|
|
SELECT ARRAY[1,2,3+4];
|
|
array
|
|
---------
|
|
{1,2,7}
|
|
(1 row)
|
|
</programlisting>
|
|
By default,
|
|
the array element type is the common type of the member expressions,
|
|
determined using the same rules as for <literal>UNION</> or
|
|
<literal>CASE</> constructs (see <xref linkend="typeconv-union-case">).
|
|
You can override this by explicitly casting the array constructor to the
|
|
desired type, for example:
|
|
<programlisting>
|
|
SELECT ARRAY[1,2,22.7]::integer[];
|
|
array
|
|
----------
|
|
{1,2,23}
|
|
(1 row)
|
|
</programlisting>
|
|
This has the same effect as casting each expression to the array
|
|
element type individually.
|
|
For more on casting, see <xref linkend="sql-syntax-type-casts">.
|
|
</para>
|
|
|
|
<para>
|
|
Multidimensional array values can be built by nesting array
|
|
constructors.
|
|
In the inner constructors, the key word <literal>ARRAY</literal> can
|
|
be omitted. For example, these produce the same result:
|
|
|
|
<programlisting>
|
|
SELECT ARRAY[ARRAY[1,2], ARRAY[3,4]];
|
|
array
|
|
---------------
|
|
{{1,2},{3,4}}
|
|
(1 row)
|
|
|
|
SELECT ARRAY[[1,2],[3,4]];
|
|
array
|
|
---------------
|
|
{{1,2},{3,4}}
|
|
(1 row)
|
|
</programlisting>
|
|
|
|
Since multidimensional arrays must be rectangular, inner constructors
|
|
at the same level must produce sub-arrays of identical dimensions.
|
|
Any cast applied to the outer <literal>ARRAY</> constructor propagates
|
|
automatically to all the inner constructors.
|
|
</para>
|
|
|
|
<para>
|
|
Multidimensional array constructor elements can be anything yielding
|
|
an array of the proper kind, not only a sub-<literal>ARRAY</> construct.
|
|
For example:
|
|
<programlisting>
|
|
CREATE TABLE arr(f1 int[], f2 int[]);
|
|
|
|
INSERT INTO arr VALUES (ARRAY[[1,2],[3,4]], ARRAY[[5,6],[7,8]]);
|
|
|
|
SELECT ARRAY[f1, f2, '{{9,10},{11,12}}'::int[]] FROM arr;
|
|
array
|
|
------------------------------------------------
|
|
{{{1,2},{3,4}},{{5,6},{7,8}},{{9,10},{11,12}}}
|
|
(1 row)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
You can construct an empty array, but since it's impossible to have an
|
|
array with no type, you must explicitly cast your empty array to the
|
|
desired type. For example:
|
|
<programlisting>
|
|
SELECT ARRAY[]::integer[];
|
|
array
|
|
-------
|
|
{}
|
|
(1 row)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
It is also possible to construct an array from the results of a
|
|
subquery. In this form, the array constructor is written with the
|
|
key word <literal>ARRAY</literal> followed by a parenthesized (not
|
|
bracketed) subquery. For example:
|
|
<programlisting>
|
|
SELECT ARRAY(SELECT oid FROM pg_proc WHERE proname LIKE 'bytea%');
|
|
?column?
|
|
-------------------------------------------------------------
|
|
{2011,1954,1948,1952,1951,1244,1950,2005,1949,1953,2006,31}
|
|
(1 row)
|
|
</programlisting>
|
|
The subquery must return a single column. The resulting
|
|
one-dimensional array will have an element for each row in the
|
|
subquery result, with an element type matching that of the
|
|
subquery's output column.
|
|
</para>
|
|
|
|
<para>
|
|
The subscripts of an array value built with <literal>ARRAY</literal>
|
|
always begin with one. For more information about arrays, see
|
|
<xref linkend="arrays">.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-row-constructors">
|
|
<title>Row Constructors</title>
|
|
|
|
<indexterm>
|
|
<primary>composite type</primary>
|
|
<secondary>constructor</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>row type</primary>
|
|
<secondary>constructor</secondary>
|
|
</indexterm>
|
|
|
|
<indexterm>
|
|
<primary>ROW</primary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
A row constructor is an expression that builds a row value (also
|
|
called a composite value) using values
|
|
for its member fields. A row constructor consists of the key word
|
|
<literal>ROW</literal>, a left parenthesis, zero or more
|
|
expressions (separated by commas) for the row field values, and finally
|
|
a right parenthesis. For example:
|
|
<programlisting>
|
|
SELECT ROW(1,2.5,'this is a test');
|
|
</programlisting>
|
|
The key word <literal>ROW</> is optional when there is more than one
|
|
expression in the list.
|
|
</para>
|
|
|
|
<para>
|
|
A row constructor can include the syntax
|
|
<replaceable>rowvalue</replaceable><literal>.*</literal>,
|
|
which will be expanded to a list of the elements of the row value,
|
|
just as occurs when the <literal>.*</> syntax is used at the top level
|
|
of a <command>SELECT</> list. For example, if table <literal>t</> has
|
|
columns <literal>f1</> and <literal>f2</>, these are the same:
|
|
<programlisting>
|
|
SELECT ROW(t.*, 42) FROM t;
|
|
SELECT ROW(t.f1, t.f2, 42) FROM t;
|
|
</programlisting>
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
Before <productname>PostgreSQL</productname> 8.2, the
|
|
<literal>.*</literal> syntax was not expanded, so that writing
|
|
<literal>ROW(t.*, 42)</> created a two-field row whose first field
|
|
was another row value. The new behavior is usually more useful.
|
|
If you need the old behavior of nested row values, write the inner
|
|
row value without <literal>.*</literal>, for instance
|
|
<literal>ROW(t, 42)</>.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
By default, the value created by a <literal>ROW</> expression is of
|
|
an anonymous record type. If necessary, it can be cast to a named
|
|
composite type — either the row type of a table, or a composite type
|
|
created with <command>CREATE TYPE AS</>. An explicit cast might be needed
|
|
to avoid ambiguity. For example:
|
|
<programlisting>
|
|
CREATE TABLE mytable(f1 int, f2 float, f3 text);
|
|
|
|
CREATE FUNCTION getf1(mytable) RETURNS int AS 'SELECT $1.f1' LANGUAGE SQL;
|
|
|
|
-- No cast needed since only one getf1() exists
|
|
SELECT getf1(ROW(1,2.5,'this is a test'));
|
|
getf1
|
|
-------
|
|
1
|
|
(1 row)
|
|
|
|
CREATE TYPE myrowtype AS (f1 int, f2 text, f3 numeric);
|
|
|
|
CREATE FUNCTION getf1(myrowtype) RETURNS int AS 'SELECT $1.f1' LANGUAGE SQL;
|
|
|
|
-- Now we need a cast to indicate which function to call:
|
|
SELECT getf1(ROW(1,2.5,'this is a test'));
|
|
ERROR: function getf1(record) is not unique
|
|
|
|
SELECT getf1(ROW(1,2.5,'this is a test')::mytable);
|
|
getf1
|
|
-------
|
|
1
|
|
(1 row)
|
|
|
|
SELECT getf1(CAST(ROW(11,'this is a test',2.5) AS myrowtype));
|
|
getf1
|
|
-------
|
|
11
|
|
(1 row)
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Row constructors can be used to build composite values to be stored
|
|
in a composite-type table column, or to be passed to a function that
|
|
accepts a composite parameter. Also,
|
|
it is possible to compare two row values or test a row with
|
|
<literal>IS NULL</> or <literal>IS NOT NULL</>, for example:
|
|
<programlisting>
|
|
SELECT ROW(1,2.5,'this is a test') = ROW(1, 3, 'not the same');
|
|
|
|
SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows
|
|
</programlisting>
|
|
For more detail see <xref linkend="functions-comparisons">.
|
|
Row constructors can also be used in connection with subqueries,
|
|
as discussed in <xref linkend="functions-subquery">.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="syntax-express-eval">
|
|
<title>Expression Evaluation Rules</title>
|
|
|
|
<indexterm>
|
|
<primary>expression</primary>
|
|
<secondary>order of evaluation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
The order of evaluation of subexpressions is not defined. In
|
|
particular, the inputs of an operator or function are not necessarily
|
|
evaluated left-to-right or in any other fixed order.
|
|
</para>
|
|
|
|
<para>
|
|
Furthermore, if the result of an expression can be determined by
|
|
evaluating only some parts of it, then other subexpressions
|
|
might not be evaluated at all. For instance, if one wrote:
|
|
<programlisting>
|
|
SELECT true OR somefunc();
|
|
</programlisting>
|
|
then <literal>somefunc()</literal> would (probably) not be called
|
|
at all. The same would be the case if one wrote:
|
|
<programlisting>
|
|
SELECT somefunc() OR true;
|
|
</programlisting>
|
|
Note that this is not the same as the left-to-right
|
|
<quote>short-circuiting</quote> of Boolean operators that is found
|
|
in some programming languages.
|
|
</para>
|
|
|
|
<para>
|
|
As a consequence, it is unwise to use functions with side effects
|
|
as part of complex expressions. It is particularly dangerous to
|
|
rely on side effects or evaluation order in <literal>WHERE</> and <literal>HAVING</> clauses,
|
|
since those clauses are extensively reprocessed as part of
|
|
developing an execution plan. Boolean
|
|
expressions (<literal>AND</>/<literal>OR</>/<literal>NOT</> combinations) in those clauses can be reorganized
|
|
in any manner allowed by the laws of Boolean algebra.
|
|
</para>
|
|
|
|
<para>
|
|
When it is essential to force evaluation order, a <literal>CASE</>
|
|
construct (see <xref linkend="functions-conditional">) can be
|
|
used. For example, this is an untrustworthy way of trying to
|
|
avoid division by zero in a <literal>WHERE</> clause:
|
|
<programlisting>
|
|
SELECT ... WHERE x > 0 AND y/x > 1.5;
|
|
</programlisting>
|
|
But this is safe:
|
|
<programlisting>
|
|
SELECT ... WHERE CASE WHEN x > 0 THEN y/x > 1.5 ELSE false END;
|
|
</programlisting>
|
|
A <literal>CASE</> construct used in this fashion will defeat optimization
|
|
attempts, so it should only be done when necessary. (In this particular
|
|
example, it would be better to sidestep the problem by writing
|
|
<literal>y > 1.5*x</> instead.)
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="sql-syntax-calling-funcs">
|
|
<title>Calling Functions</title>
|
|
|
|
<indexterm zone="sql-syntax-calling-funcs">
|
|
<primary>notation</primary>
|
|
<secondary>functions</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> allows functions that have named
|
|
parameters to be called using either <firstterm>positional</firstterm> or
|
|
<firstterm>named</firstterm> notation. Named notation is especially
|
|
useful for functions that have a large number of parameters, since it
|
|
makes the associations between parameters and actual arguments more
|
|
explicit and reliable.
|
|
In positional notation, a function call is written with
|
|
its argument values in the same order as they are defined in the function
|
|
declaration. In named notation, the arguments are matched to the
|
|
function parameters by name and can be written in any order.
|
|
</para>
|
|
|
|
<para>
|
|
In either notation, parameters that have default values given in the
|
|
function declaration need not be written in the call at all. But this
|
|
is particularly useful in named notation, since any combination of
|
|
parameters can be omitted; while in positional notation parameters can
|
|
only be omitted from right to left.
|
|
</para>
|
|
|
|
<para>
|
|
<productname>PostgreSQL</productname> also supports
|
|
<firstterm>mixed</firstterm> notation, which combines positional and
|
|
named notation. In this case, positional parameters are written first
|
|
and named parameters appear after them.
|
|
</para>
|
|
|
|
<para>
|
|
The following examples will illustrate the usage of all three
|
|
notations, using the following function definition:
|
|
<programlisting>
|
|
CREATE FUNCTION concat_lower_or_upper(a text, b text, uppercase boolean DEFAULT false)
|
|
RETURNS text
|
|
AS
|
|
$$
|
|
SELECT CASE
|
|
WHEN $3 THEN UPPER($1 || ' ' || $2)
|
|
ELSE LOWER($1 || ' ' || $2)
|
|
END;
|
|
$$
|
|
LANGUAGE SQL IMMUTABLE STRICT;
|
|
</programlisting>
|
|
Function <function>concat_lower_or_upper</function> has two mandatory
|
|
parameters, <literal>a</literal> and <literal>b</literal>. Additionally
|
|
there is one optional parameter <literal>uppercase</literal> which defaults
|
|
to <literal>false</literal>. The <literal>a</literal> and
|
|
<literal>b</literal> inputs will be concatenated, and forced to either
|
|
upper or lower case depending on the <literal>uppercase</literal>
|
|
parameter. The remaining details of this function
|
|
definition are not important here (see <xref linkend="extend"> for
|
|
more information).
|
|
</para>
|
|
|
|
<sect2 id="sql-syntax-calling-funcs-positional">
|
|
<title>Using positional notation</title>
|
|
|
|
<indexterm>
|
|
<primary>function</primary>
|
|
<secondary>positional notation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
Positional notation is the traditional mechanism for passing arguments
|
|
to functions in <productname>PostgreSQL</productname>. An example is:
|
|
<screen>
|
|
SELECT concat_lower_or_upper('Hello', 'World', true);
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
HELLO WORLD
|
|
(1 row)
|
|
</screen>
|
|
All arguments are specified in order. The result is upper case since
|
|
<literal>uppercase</literal> is specified as <literal>true</literal>.
|
|
Another example is:
|
|
<screen>
|
|
SELECT concat_lower_or_upper('Hello', 'World');
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
hello world
|
|
(1 row)
|
|
</screen>
|
|
Here, the <literal>uppercase</literal> parameter is omitted, so it
|
|
receives its default value of <literal>false</literal>, resulting in
|
|
lower case output. In positional notation, arguments can be omitted
|
|
from right to left so long as they have defaults.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-calling-funcs-named">
|
|
<title>Using named notation</title>
|
|
|
|
<indexterm>
|
|
<primary>function</primary>
|
|
<secondary>named notation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
In named notation, each argument's name is specified using the
|
|
<literal>AS</literal> keyword. For example:
|
|
<screen>
|
|
SELECT concat_lower_or_upper('Hello' AS a, 'World' AS b);
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
hello world
|
|
(1 row)
|
|
</screen>
|
|
Again, the argument <literal>uppercase</literal> was omitted
|
|
so it is set to <literal>false</literal> implicitly. One advantage of
|
|
using named notation is that the arguments may be specified in any
|
|
order, for example:
|
|
<screen>
|
|
SELECT concat_lower_or_upper('Hello' AS a, 'World' AS b, true AS uppercase);
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
HELLO WORLD
|
|
(1 row)
|
|
|
|
SELECT concat_lower_or_upper('Hello' AS a, true AS uppercase, 'World' AS b);
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
HELLO WORLD
|
|
(1 row)
|
|
</screen>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="sql-syntax-calling-funcs-mixed">
|
|
<title>Using mixed notation</title>
|
|
|
|
<indexterm>
|
|
<primary>function</primary>
|
|
<secondary>mixed notation</secondary>
|
|
</indexterm>
|
|
|
|
<para>
|
|
The mixed notation combines positional and named notation. However, as
|
|
already mentioned, named arguments cannot precede positional arguments.
|
|
For example:
|
|
<screen>
|
|
SELECT concat_lower_or_upper('Hello', 'World', true AS uppercase);
|
|
concat_lower_or_upper
|
|
-----------------------
|
|
HELLO WORLD
|
|
(1 row)
|
|
</screen>
|
|
In the above query, the arguments <literal>a</literal> and
|
|
<literal>b</literal> are specified positionally, while
|
|
<literal>uppercase</> is specified by name. In this example,
|
|
that adds little except documentation. With a more complex function
|
|
having numerous parameters that have default values, named or mixed
|
|
notation can save a great deal of writing and reduce chances for error.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
</chapter>
|