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Tom Lane 2003-11-04 00:34:50 +00:00
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doc/src/sgml/ref/select.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.71 2003/11/01 01:56:29 petere Exp $ $Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.71.2.1 2003/11/04 00:34:50 tgl Exp $
PostgreSQL documentation PostgreSQL documentation
--> -->
@ -41,11 +41,6 @@ where <replaceable class="parameter">from_item</replaceable> can be one of:
<replaceable class="parameter">from_item</replaceable> [ NATURAL ] <replaceable class="parameter">join_type</replaceable> <replaceable class="parameter">from_item</replaceable> [ ON <replaceable class="parameter">join_condition</replaceable> | USING ( <replaceable class="parameter">join_column</replaceable> [, ...] ) ] <replaceable class="parameter">from_item</replaceable> [ NATURAL ] <replaceable class="parameter">join_type</replaceable> <replaceable class="parameter">from_item</replaceable> [ ON <replaceable class="parameter">join_condition</replaceable> | USING ( <replaceable class="parameter">join_column</replaceable> [, ...] ) ]
</synopsis> </synopsis>
<comment>FIXME: This last syntax is incorrect if the join type is an
INNER or OUTER join (in which case one of NATURAL, ON ..., or USING
... is mandatory, not optional). What's the best way to fix
this?</comment>
</refsynopsisdiv> </refsynopsisdiv>
<refsect1> <refsect1>
@ -107,7 +102,7 @@ this?</comment>
<listitem> <listitem>
<para> <para>
The actual output rows are computed the The actual output rows are computed using the
<command>SELECT</command> output expressions for each selected <command>SELECT</command> output expressions for each selected
row. (See row. (See
<xref linkend="sql-select-list" endterm="sql-select-list-title"> <xref linkend="sql-select-list" endterm="sql-select-list-title">
@ -125,15 +120,6 @@ this?</comment>
</para> </para>
</listitem> </listitem>
<listitem>
<para>
If the <literal>LIMIT</literal> or <literal>OFFSET</literal>
clause is specified, the <command>SELECT</command> statement
only returns a subset of the result rows. (See <xref
linkend="sql-limit" endterm="sql-limit-title"> below.)
</para>
</listitem>
<listitem> <listitem>
<para> <para>
<literal>DISTINCT</literal> eliminates duplicate rows from the <literal>DISTINCT</literal> eliminates duplicate rows from the
@ -145,6 +131,15 @@ this?</comment>
</para> </para>
</listitem> </listitem>
<listitem>
<para>
If the <literal>LIMIT</literal> or <literal>OFFSET</literal>
clause is specified, the <command>SELECT</command> statement
only returns a subset of the result rows. (See <xref
linkend="sql-limit" endterm="sql-limit-title"> below.)
</para>
</listitem>
<listitem> <listitem>
<para> <para>
The <literal>FOR UPDATE</literal> clause causes the The <literal>FOR UPDATE</literal> clause causes the
@ -291,17 +286,21 @@ this?</comment>
</para> </para>
<para> <para>
A <literal>JOIN</literal> clause, combines two A <literal>JOIN</literal> clause combines two
<literal>FROM</> items. (Use parentheses if necessary to <literal>FROM</> items. Use parentheses if necessary to
determine the order of nesting.) determine the order of nesting. In the absence of parentheses,
<literal>JOIN</literal>s nest left-to-right. In any case
<literal>JOIN</literal> binds more tightly than the commas
separating <literal>FROM</> items.
</para> </para>
<para> <para>
<literal>CROSS JOIN</> and <literal>INNER JOIN</literal> <literal>CROSS JOIN</> and <literal>INNER JOIN</literal>
produce a simple Cartesian product, the same as you get from produce a simple Cartesian product, the same result as you get from
listing the two items at the top level of <literal>FROM</>. listing the two items at the top level of <literal>FROM</>,
but restricted by the join condition (if any).
<literal>CROSS JOIN</> is equivalent to <literal>INNER JOIN ON <literal>CROSS JOIN</> is equivalent to <literal>INNER JOIN ON
(true)</>, that is, no rows are removed by qualification. (TRUE)</>, that is, no rows are removed by qualification.
These join types are just a notational convenience, since they These join types are just a notational convenience, since they
do nothing you couldn't do with plain <literal>FROM</> and do nothing you couldn't do with plain <literal>FROM</> and
<literal>WHERE</>. <literal>WHERE</>.
@ -315,7 +314,7 @@ this?</comment>
condition. This left-hand row is extended to the full width condition. This left-hand row is extended to the full width
of the joined table by inserting null values for the of the joined table by inserting null values for the
right-hand columns. Note that only the <literal>JOIN</> right-hand columns. Note that only the <literal>JOIN</>
clauses own condition is considered while deciding which rows clause's own condition is considered while deciding which rows
have matches. Outer conditions are applied afterwards. have matches. Outer conditions are applied afterwards.
</para> </para>
@ -410,7 +409,7 @@ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...]
expressions. <replaceable expressions. <replaceable
class="parameter">expression</replaceable> can be an input column class="parameter">expression</replaceable> can be an input column
name, or the name or ordinal number of an output column name, or the name or ordinal number of an output column
(<command>SELECT</command> list), or it can be an arbitrary (<command>SELECT</command> list item), or an arbitrary
expression formed from input-column values. In case of ambiguity, expression formed from input-column values. In case of ambiguity,
a <literal>GROUP BY</literal> name will be interpreted as an a <literal>GROUP BY</literal> name will be interpreted as an
input-column name rather than an output column name. input-column name rather than an output column name.
@ -497,7 +496,7 @@ HAVING <replaceable class="parameter">condition</replaceable>
<para> <para>
Currently, <literal>FOR UPDATE</> may not be specified either for Currently, <literal>FOR UPDATE</> may not be specified either for
a <literal>UNION</> result or for the inputs of <literal>UNION</>. a <literal>UNION</> result or for any input of a <literal>UNION</>.
</para> </para>
</refsect2> </refsect2>
@ -613,7 +612,7 @@ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC |
</synopsis> </synopsis>
<replaceable class="parameter">expression</replaceable> can be the <replaceable class="parameter">expression</replaceable> can be the
name or ordinal number of an output column name or ordinal number of an output column
(<command>SELECT</command> list), or it can be an arbitrary (<command>SELECT</command> list item), or it can be an arbitrary
expression formed from input-column values. expression formed from input-column values.
</para> </para>
@ -623,7 +622,7 @@ ORDER BY <replaceable class="parameter">expression</replaceable> [ ASC | DESC |
equal according to the leftmost expression, the are compared equal according to the leftmost expression, the are compared
according to the next expression and so on. If they are equal according to the next expression and so on. If they are equal
according to all specified expressions, they are returned in according to all specified expressions, they are returned in
random order. an implementation-dependent order.
</para> </para>
<para> <para>
@ -660,7 +659,7 @@ SELECT name FROM distributors ORDER BY code;
<para> <para>
Optionally one may add the key word <literal>ASC</> (ascending) or Optionally one may add the key word <literal>ASC</> (ascending) or
<literal>DESC</> (descending) after each expression in the <literal>DESC</> (descending) after any expression in the
<literal>ORDER BY</> clause. If not specified, <literal>ASC</> is <literal>ORDER BY</> clause. If not specified, <literal>ASC</> is
assumed by default. Alternatively, a specific ordering operator assumed by default. Alternatively, a specific ordering operator
name may be specified in the <literal>USING</> clause. name may be specified in the <literal>USING</> clause.
@ -689,15 +688,18 @@ SELECT name FROM distributors ORDER BY code;
<para> <para>
The <literal>LIMIT</literal> clause consists of two independent The <literal>LIMIT</literal> clause consists of two independent
clauses: sub-clauses:
<synopsis> <synopsis>
LIMIT { <replaceable class="parameter">count</replaceable> | ALL } LIMIT { <replaceable class="parameter">count</replaceable> | ALL }
OFFSET <replaceable class="parameter">start</replaceable> OFFSET <replaceable class="parameter">start</replaceable>
</synopsis> </synopsis>
<replaceable class="parameter">count</replaceable> specifies the <replaceable class="parameter">count</replaceable> specifies the
maximum number of rows to return, and <replaceable maximum number of rows to return, while <replaceable
class="parameter">start</replaceable> specifies the number of rows class="parameter">start</replaceable> specifies the number of rows
to skip before starting to return rows. to skip before starting to return rows. When both are specified,
<replaceable class="parameter">start</replaceable> rows are skipped
before starting to count the <replaceable
class="parameter">count</replaceable> rows to be returned.
</para> </para>
<para> <para>
@ -754,6 +756,13 @@ SELECT DISTINCT ON (location) location, time, report
of time values for each location, we'd have gotten a report from of time values for each location, we'd have gotten a report from
an unpredictable time for each location. an unpredictable time for each location.
</para> </para>
<para>
The <literal>DISTINCT ON</> expression(s) must match the leftmost
<literal>ORDER BY</> expression(s). The <literal>ORDER BY</> clause
will normally contain additional expression(s) that determine the
desired precedence of rows within each <literal>DISTINCT ON</> group.
</para>
</refsect2> </refsect2>
<refsect2 id="SQL-FOR-UPDATE"> <refsect2 id="SQL-FOR-UPDATE">
@ -889,10 +898,10 @@ SELECT * FROM distributors ORDER BY 2;
</para> </para>
<para> <para>
This example shows how to obtain the union of the tables The next example shows how to obtain the union of the tables
<literal>distributors</literal> and <literal>distributors</literal> and
<literal>actors</literal>, restricting the results to those that begin <literal>actors</literal>, restricting the results to those that begin
with letter W in each table. Only distinct rows are wanted, so the with the letter W in each table. Only distinct rows are wanted, so the
key word <literal>ALL</literal> is omitted. key word <literal>ALL</literal> is omitted.
<programlisting> <programlisting>
@ -925,7 +934,7 @@ SELECT actors.name
<para> <para>
This example shows how to use a function in the <literal>FROM</> This example shows how to use a function in the <literal>FROM</>
clause, both with and without a column definition list. clause, both with and without a column definition list:
<programlisting> <programlisting>
CREATE FUNCTION distributors(int) RETURNS SETOF distributors AS ' CREATE FUNCTION distributors(int) RETURNS SETOF distributors AS '
@ -1048,7 +1057,8 @@ SELECT distributors.* FROM distributors d, distributors distributors;
</para> </para>
<para> <para>
SQL99 uses a slightly different definition which is not upward compatible SQL99 uses a slightly different definition which is not entirely upward
compatible
with SQL92. In most cases, however, <productname>PostgreSQL</productname> with SQL92. In most cases, however, <productname>PostgreSQL</productname>
will interpret an <literal>ORDER BY</literal> or <literal>GROUP will interpret an <literal>ORDER BY</literal> or <literal>GROUP
BY</literal> expression the same way SQL99 does. BY</literal> expression the same way SQL99 does.