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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.23. Subquery Expressions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="functions-window.html" title="9.22. Window Functions" /><link rel="next" href="functions-comparisons.html" title="9.24. Row and Array Comparisons" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.23. Subquery Expressions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-window.html" title="9.22. Window Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-comparisons.html" title="9.24. Row and Array Comparisons">Next</a></td></tr></table><hr /></div><div class="sect1" id="FUNCTIONS-SUBQUERY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.23. Subquery Expressions <a href="#FUNCTIONS-SUBQUERY" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-EXISTS">9.23.1. <code class="literal">EXISTS</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-IN">9.23.2. <code class="literal">IN</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-NOTIN">9.23.3. <code class="literal">NOT IN</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-ANY-SOME">9.23.4. <code class="literal">ANY</code>/<code class="literal">SOME</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-ALL">9.23.5. <code class="literal">ALL</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-SINGLE-ROW-COMP">9.23.6. Single-Row Comparison</a></span></dt></dl></div><a id="id-1.5.8.29.2" class="indexterm"></a><a id="id-1.5.8.29.3" class="indexterm"></a><a id="id-1.5.8.29.4" class="indexterm"></a><a id="id-1.5.8.29.5" class="indexterm"></a><a id="id-1.5.8.29.6" class="indexterm"></a><a id="id-1.5.8.29.7" class="indexterm"></a><a id="id-1.5.8.29.8" class="indexterm"></a><p>
This section describes the <acronym class="acronym">SQL</acronym>-compliant subquery
expressions available in <span class="productname">PostgreSQL</span>.
All of the expression forms documented in this section return
Boolean (true/false) results.
</p><div class="sect2" id="FUNCTIONS-SUBQUERY-EXISTS"><div class="titlepage"><div><div><h3 class="title">9.23.1. <code class="literal">EXISTS</code> <a href="#FUNCTIONS-SUBQUERY-EXISTS" class="id_link">#</a></h3></div></div></div><pre class="synopsis">
EXISTS (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The argument of <code class="token">EXISTS</code> is an arbitrary <code class="command">SELECT</code> statement,
or <em class="firstterm">subquery</em>. The
subquery is evaluated to determine whether it returns any rows.
If it returns at least one row, the result of <code class="token">EXISTS</code> is
<span class="quote">“<span class="quote">true</span>”</span>; if the subquery returns no rows, the result of <code class="token">EXISTS</code>
is <span class="quote">“<span class="quote">false</span>”</span>.
</p><p>
The subquery can refer to variables from the surrounding query,
which will act as constants during any one evaluation of the subquery.
</p><p>
The subquery will generally only be executed long enough to determine
whether at least one row is returned, not all the way to completion.
It is unwise to write a subquery that has side effects (such as
calling sequence functions); whether the side effects occur
might be unpredictable.
</p><p>
Since the result depends only on whether any rows are returned,
and not on the contents of those rows, the output list of the
subquery is normally unimportant. A common coding convention is
to write all <code class="literal">EXISTS</code> tests in the form
<code class="literal">EXISTS(SELECT 1 WHERE ...)</code>. There are exceptions to
this rule however, such as subqueries that use <code class="token">INTERSECT</code>.
</p><p>
This simple example is like an inner join on <code class="literal">col2</code>, but
it produces at most one output row for each <code class="literal">tab1</code> row,
even if there are several matching <code class="literal">tab2</code> rows:
</p><pre class="screen">
SELECT col1
FROM tab1
WHERE EXISTS (SELECT 1 FROM tab2 WHERE col2 = tab1.col2);
</pre><p>
</p></div><div class="sect2" id="FUNCTIONS-SUBQUERY-IN"><div class="titlepage"><div><div><h3 class="title">9.23.2. <code class="literal">IN</code> <a href="#FUNCTIONS-SUBQUERY-IN" class="id_link">#</a></h3></div></div></div><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> IN (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <code class="token">IN</code> is <span class="quote">“<span class="quote">true</span>”</span> if any equal subquery row is found.
The result is <span class="quote">“<span class="quote">false</span>”</span> if no equal row is found (including the
case where the subquery returns no rows).
</p><p>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <code class="token">IN</code> construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</p><p>
As with <code class="token">EXISTS</code>, it's unwise to assume that the subquery will
be evaluated completely.
</p><pre class="synopsis">
<em class="replaceable"><code>row_constructor</code></em> IN (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The left-hand side of this form of <code class="token">IN</code> is a row constructor,
as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <code class="token">IN</code> is <span class="quote">“<span class="quote">true</span>”</span> if any equal subquery row is found.
The result is <span class="quote">“<span class="quote">false</span>”</span> if no equal row is found (including the
case where the subquery returns no rows).
</p><p>
As usual, null values in the rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the per-row results are either unequal or null, with at least one
null, then the result of <code class="token">IN</code> is null.
</p></div><div class="sect2" id="FUNCTIONS-SUBQUERY-NOTIN"><div class="titlepage"><div><div><h3 class="title">9.23.3. <code class="literal">NOT IN</code> <a href="#FUNCTIONS-SUBQUERY-NOTIN" class="id_link">#</a></h3></div></div></div><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> NOT IN (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result.
The result of <code class="token">NOT IN</code> is <span class="quote">“<span class="quote">true</span>”</span> if only unequal subquery rows
are found (including the case where the subquery returns no rows).
The result is <span class="quote">“<span class="quote">false</span>”</span> if any equal row is found.
</p><p>
Note that if the left-hand expression yields null, or if there are
no equal right-hand values and at least one right-hand row yields
null, the result of the <code class="token">NOT IN</code> construct will be null, not true.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</p><p>
As with <code class="token">EXISTS</code>, it's unwise to assume that the subquery will
be evaluated completely.
</p><pre class="synopsis">
<em class="replaceable"><code>row_constructor</code></em> NOT IN (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The left-hand side of this form of <code class="token">NOT IN</code> is a row constructor,
as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result.
The result of <code class="token">NOT IN</code> is <span class="quote">“<span class="quote">true</span>”</span> if only unequal subquery rows
are found (including the case where the subquery returns no rows).
The result is <span class="quote">“<span class="quote">false</span>”</span> if any equal row is found.
</p><p>
As usual, null values in the rows are combined per
the normal rules of SQL Boolean expressions. Two rows are considered
equal if all their corresponding members are non-null and equal; the rows
are unequal if any corresponding members are non-null and unequal;
otherwise the result of that row comparison is unknown (null).
If all the per-row results are either unequal or null, with at least one
null, then the result of <code class="token">NOT IN</code> is null.
</p></div><div class="sect2" id="FUNCTIONS-SUBQUERY-ANY-SOME"><div class="titlepage"><div><div><h3 class="title">9.23.4. <code class="literal">ANY</code>/<code class="literal">SOME</code> <a href="#FUNCTIONS-SUBQUERY-ANY-SOME" class="id_link">#</a></h3></div></div></div><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> ANY (<em class="replaceable"><code>subquery</code></em>)
<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> SOME (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <em class="replaceable"><code>operator</code></em>, which must yield a Boolean
result.
The result of <code class="token">ANY</code> is <span class="quote">“<span class="quote">true</span>”</span> if any true result is obtained.
The result is <span class="quote">“<span class="quote">false</span>”</span> if no true result is found (including the
case where the subquery returns no rows).
</p><p>
<code class="token">SOME</code> is a synonym for <code class="token">ANY</code>.
<code class="token">IN</code> is equivalent to <code class="literal">= ANY</code>.
</p><p>
Note that if there are no successes and at least one right-hand row yields
null for the operator's result, the result of the <code class="token">ANY</code> construct
will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</p><p>
As with <code class="token">EXISTS</code>, it's unwise to assume that the subquery will
be evaluated completely.
</p><pre class="synopsis">
<em class="replaceable"><code>row_constructor</code></em> <em class="replaceable"><code>operator</code></em> ANY (<em class="replaceable"><code>subquery</code></em>)
<em class="replaceable"><code>row_constructor</code></em> <em class="replaceable"><code>operator</code></em> SOME (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The left-hand side of this form of <code class="token">ANY</code> is a row constructor,
as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <em class="replaceable"><code>operator</code></em>.
The result of <code class="token">ANY</code> is <span class="quote">“<span class="quote">true</span>”</span> if the comparison
returns true for any subquery row.
The result is <span class="quote">“<span class="quote">false</span>”</span> if the comparison returns false for every
subquery row (including the case where the subquery returns no
rows).
The result is NULL if no comparison with a subquery row returns true,
and at least one comparison returns NULL.
</p><p>
See <a class="xref" href="functions-comparisons.html#ROW-WISE-COMPARISON" title="9.24.5. Row Constructor Comparison">Section 9.24.5</a> for details about the meaning
of a row constructor comparison.
</p></div><div class="sect2" id="FUNCTIONS-SUBQUERY-ALL"><div class="titlepage"><div><div><h3 class="title">9.23.5. <code class="literal">ALL</code> <a href="#FUNCTIONS-SUBQUERY-ALL" class="id_link">#</a></h3></div></div></div><pre class="synopsis">
<em class="replaceable"><code>expression</code></em> <em class="replaceable"><code>operator</code></em> ALL (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The right-hand side is a parenthesized
subquery, which must return exactly one column. The left-hand expression
is evaluated and compared to each row of the subquery result using the
given <em class="replaceable"><code>operator</code></em>, which must yield a Boolean
result.
The result of <code class="token">ALL</code> is <span class="quote">“<span class="quote">true</span>”</span> if all rows yield true
(including the case where the subquery returns no rows).
The result is <span class="quote">“<span class="quote">false</span>”</span> if any false result is found.
The result is NULL if no comparison with a subquery row returns false,
and at least one comparison returns NULL.
</p><p>
<code class="token">NOT IN</code> is equivalent to <code class="literal"><> ALL</code>.
</p><p>
As with <code class="token">EXISTS</code>, it's unwise to assume that the subquery will
be evaluated completely.
</p><pre class="synopsis">
<em class="replaceable"><code>row_constructor</code></em> <em class="replaceable"><code>operator</code></em> ALL (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The left-hand side of this form of <code class="token">ALL</code> is a row constructor,
as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>.
The right-hand side is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand row. The left-hand expressions are
evaluated and compared row-wise to each row of the subquery result,
using the given <em class="replaceable"><code>operator</code></em>.
The result of <code class="token">ALL</code> is <span class="quote">“<span class="quote">true</span>”</span> if the comparison
returns true for all subquery rows (including the
case where the subquery returns no rows).
The result is <span class="quote">“<span class="quote">false</span>”</span> if the comparison returns false for any
subquery row.
The result is NULL if no comparison with a subquery row returns false,
and at least one comparison returns NULL.
</p><p>
See <a class="xref" href="functions-comparisons.html#ROW-WISE-COMPARISON" title="9.24.5. Row Constructor Comparison">Section 9.24.5</a> for details about the meaning
of a row constructor comparison.
</p></div><div class="sect2" id="FUNCTIONS-SUBQUERY-SINGLE-ROW-COMP"><div class="titlepage"><div><div><h3 class="title">9.23.6. Single-Row Comparison <a href="#FUNCTIONS-SUBQUERY-SINGLE-ROW-COMP" class="id_link">#</a></h3></div></div></div><a id="id-1.5.8.29.15.2" class="indexterm"></a><pre class="synopsis">
<em class="replaceable"><code>row_constructor</code></em> <em class="replaceable"><code>operator</code></em> (<em class="replaceable"><code>subquery</code></em>)
</pre><p>
The left-hand side is a row constructor,
as described in <a class="xref" href="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS" title="4.2.13. Row Constructors">Section 4.2.13</a>.
The right-hand side is a parenthesized subquery, which must return exactly
as many columns as there are expressions in the left-hand row. Furthermore,
the subquery cannot return more than one row. (If it returns zero rows,
the result is taken to be null.) The left-hand side is evaluated and
compared row-wise to the single subquery result row.
</p><p>
See <a class="xref" href="functions-comparisons.html#ROW-WISE-COMPARISON" title="9.24.5. Row Constructor Comparison">Section 9.24.5</a> for details about the meaning
of a row constructor comparison.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-window.html" title="9.22. Window Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-comparisons.html" title="9.24. Row and Array Comparisons">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.22. Window Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.24. Row and Array Comparisons</td></tr></table></div></body></html>
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