1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
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 xmlns="http://www.w3.org/TR/xhtml1/transitional" 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 14.5 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></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 xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></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 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.24. Row and Array Comparisons</td></tr></table></div></body></html>
|
