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Add Oracle-compatible GREATEST and LEAST functions. Pavel Stehule

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This commit is contained in:
Tom Lane
2005-06-26 22:05:42 +00:00
parent d395aecffa
commit 943b396245
17 changed files with 409 additions and 36 deletions
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35
doc/src/sgml/func.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.259 2005/06/24 20:53:29 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.260 2005/06/26 22:05:35 tgl Exp $
PostgreSQL documentation
-->
@ -6901,6 +6901,39 @@ SELECT NULLIF(value, '(none)') ...
</sect2>
<sect2>
<title><literal>GREATEST</literal> and <literal>LEAST</literal></title>
<indexterm>
<primary>GREATEST</primary>
</indexterm>
<indexterm>
<primary>LEAST</primary>
</indexterm>
<synopsis>
<function>GREATEST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<synopsis>
<function>LEAST</function>(<replaceable>value</replaceable> <optional>, ...</optional>)
</synopsis>
<para>
The <function>GREATEST</> and <function>LEAST</> functions select the
largest or smallest value from a list of any number of expressions.
The expressions must all be convertible to a common data type, which
will be the type of the result
(see <xref linkend="typeconv-union-case"> for details). NULL values
in the list are ignored. The result will be NULL only if all the
expressions evaluate to NULL.
</para>
<para>
Note that <function>GREATEST</> and <function>LEAST</> are not in
the SQL standard, but are a common extension.
</para>
</sect2>
</sect1>

26
doc/src/sgml/typeconv.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.43 2004/12/23 23:07:38 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.44 2005/06/26 22:05:36 tgl Exp $
-->
<chapter Id="typeconv">
@ -120,7 +120,7 @@ with, and perhaps converted to, the types of the target columns.
</varlistentry>
<varlistentry>
<term>
<literal>UNION</literal>, <literal>CASE</literal>, and <literal>ARRAY</literal> constructs
<literal>UNION</literal>, <literal>CASE</literal>, and related constructs
</term>
<listitem>
<para>
@ -129,7 +129,8 @@ must appear in a single set of columns, the types of the results of each
<command>SELECT</> clause must be matched up and converted to a uniform set.
Similarly, the result expressions of a <literal>CASE</> construct must be
converted to a common type so that the <literal>CASE</> expression as a whole
has a known output type. The same holds for <literal>ARRAY</> constructs.
has a known output type. The same holds for <literal>ARRAY</> constructs,
and for the <function>GREATEST</> and <function>LEAST</> functions.
</para>
</listitem>
</varlistentry>
@ -782,7 +783,7 @@ padding spaces.
</sect1>
<sect1 id="typeconv-union-case">
<title><literal>UNION</literal>, <literal>CASE</literal>, and <literal>ARRAY</literal> Constructs</title>
<title><literal>UNION</literal>, <literal>CASE</literal>, and Related Constructs</title>
<indexterm zone="typeconv-union-case">
<primary>UNION</primary>
@ -799,20 +800,31 @@ padding spaces.
<secondary>determination of result type</secondary>
</indexterm>
<indexterm zone="typeconv-union-case">
<primary>GREATEST</primary>
<secondary>determination of result type</secondary>
</indexterm>
<indexterm zone="typeconv-union-case">
<primary>LEAST</primary>
<secondary>determination of result type</secondary>
</indexterm>
<para>
SQL <literal>UNION</> constructs must match up possibly dissimilar
types to become a single result set. The resolution algorithm is
applied separately to each output column of a union query. The
<literal>INTERSECT</> and <literal>EXCEPT</> constructs resolve
dissimilar types in the same way as <literal>UNION</>. The
<literal>CASE</> and <literal>ARRAY</> constructs use the identical
<literal>CASE</>, <literal>ARRAY</>, <function>GREATEST</> and
<function>LEAST</> constructs use the identical
algorithm to match up their component expressions and select a result
data type.
</para>
<procedure>
<title><literal>UNION</literal>, <literal>CASE</literal>, and
<literal>ARRAY</literal> Type Resolution</title>
<title>Type Resolution for <literal>UNION</literal>, <literal>CASE</literal>,
and Related Constructs</title>
<step performance="required">
<para>