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<!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>9.22. 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 V1.79.1" /><link rel="prev" href="functions-window.html" title="9.21. Window Functions" /><link rel="next" href="functions-comparisons.html" title="9.23. Row and Array Comparisons" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.22. Subquery Expressions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-window.html" title="9.21. 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 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-comparisons.html" title="9.23. Row and Array Comparisons">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-SUBQUERY"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.22. Subquery Expressions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-EXISTS">9.22.1. <code class="literal">EXISTS</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-IN">9.22.2. <code class="literal">IN</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-NOTIN">9.22.3. <code class="literal">NOT IN</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#FUNCTIONS-SUBQUERY-ANY-SOME">9.22.4. <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">9.22.5. <code class="literal">ALL</code></a></span></dt><dt><span class="sect2"><a href="functions-subquery.html#id-1.5.8.27.15">9.22.6. Single-Row Comparison</a></span></dt></dl></div><a id="id-1.5.8.27.2" class="indexterm"></a><a id="id-1.5.8.27.3" class="indexterm"></a><a id="id-1.5.8.27.4" class="indexterm"></a><a id="id-1.5.8.27.5" class="indexterm"></a><a id="id-1.5.8.27.6" class="indexterm"></a><a id="id-1.5.8.27.7" class="indexterm"></a><a id="id-1.5.8.27.8" 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">9.22.1. <code class="literal">EXISTS</code></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">9.22.2. <code class="literal">IN</code></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">9.22.3. <code class="literal">NOT IN</code></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">9.22.4. <code class="literal">ANY</code>/<code class="literal">SOME</code></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="9.23.5. Row Constructor Comparison">Section 9.23.5</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">9.22.5. <code class="literal">ALL</code></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">&lt;&gt; 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="9.23.5. Row Constructor Comparison">Section 9.23.5</a> for details about the meaning
   of a row constructor comparison.
  </p></div><div class="sect2" id="id-1.5.8.27.15"><div class="titlepage"><div><div><h3 class="title">9.22.6. Single-Row Comparison</h3></div></div></div><a id="id-1.5.8.27.15.2" 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="9.23.5. Row Constructor Comparison">Section 9.23.5</a> for details about the meaning
   of a row constructor comparison.
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