diff options
Diffstat (limited to 'doc/src/sgml/html/functions-subquery.html')
| -rw-r--r-- | doc/src/sgml/html/functions-subquery.html | 213 |
1 files changed, 213 insertions, 0 deletions
diff --git a/doc/src/sgml/html/functions-subquery.html b/doc/src/sgml/html/functions-subquery.html new file mode 100644 index 0000000..addb6f2 --- /dev/null +++ b/doc/src/sgml/html/functions-subquery.html @@ -0,0 +1,213 @@ +<?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 15.5 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</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#id-1.5.8.29.15">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></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></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></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></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></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="id-1.5.8.29.15"><div class="titlepage"><div><div><h3 class="title">9.23.6. Single-Row Comparison</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 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.24. Row and Array Comparisons</td></tr></table></div></body></html>
\ No newline at end of file |