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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Subquery Expressions</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Functions and Operators" HREF="functions.html"><LINK REL="PREVIOUS" TITLE="Window Functions" HREF="functions-window.html"><LINK REL="NEXT" TITLE="Row and Array Comparisons" HREF="functions-comparisons.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Window Functions" HREF="functions-window.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="functions.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 9. Functions and Operators</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Row and Array Comparisons" HREF="functions-comparisons.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="FUNCTIONS-SUBQUERY" >9.22. Subquery Expressions</A ></H1 ><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" ><H2 CLASS="SECT2" ><A NAME="FUNCTIONS-SUBQUERY-EXISTS" >9.22.1. <TT CLASS="LITERAL" >EXISTS</TT ></A ></H2 ><PRE CLASS="SYNOPSIS" >EXISTS (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The argument of <TT CLASS="TOKEN" >EXISTS</TT > is an arbitrary <TT CLASS="COMMAND" >SELECT</TT > statement, or <I CLASS="FIRSTTERM" >subquery</I >. The subquery is evaluated to determine whether it returns any rows. If it returns at least one row, the result of <TT CLASS="TOKEN" >EXISTS</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN >; if the subquery returns no rows, the result of <TT CLASS="TOKEN" >EXISTS</TT > is <SPAN CLASS="QUOTE" >"false"</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 <TT CLASS="LITERAL" >EXISTS</TT > tests in the form <TT CLASS="LITERAL" >EXISTS(SELECT 1 WHERE ...)</TT >. There are exceptions to this rule however, such as subqueries that use <TT CLASS="TOKEN" >INTERSECT</TT >. </P ><P > This simple example is like an inner join on <TT CLASS="LITERAL" >col2</TT >, but it produces at most one output row for each <TT CLASS="LITERAL" >tab1</TT > row, even if there are several matching <TT CLASS="LITERAL" >tab2</TT > 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" ><H2 CLASS="SECT2" ><A NAME="FUNCTIONS-SUBQUERY-IN" >9.22.2. <TT CLASS="LITERAL" >IN</TT ></A ></H2 ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >expression</I ></TT > IN (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</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 <TT CLASS="TOKEN" >IN</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if any equal subquery row is found. The result is <SPAN CLASS="QUOTE" >"false"</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 <TT CLASS="TOKEN" >IN</TT > 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 <TT CLASS="TOKEN" >EXISTS</TT >, it's unwise to assume that the subquery will be evaluated completely. </P ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > IN (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The left-hand side of this form of <TT CLASS="TOKEN" >IN</TT > is a row constructor, as described in <A HREF="sql-expressions.html#SQL-SYNTAX-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 <TT CLASS="TOKEN" >IN</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if any equal subquery row is found. The result is <SPAN CLASS="QUOTE" >"false"</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 <TT CLASS="TOKEN" >IN</TT > is null. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="FUNCTIONS-SUBQUERY-NOTIN" >9.22.3. <TT CLASS="LITERAL" >NOT IN</TT ></A ></H2 ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >expression</I ></TT > NOT IN (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</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 <TT CLASS="TOKEN" >NOT IN</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if only unequal subquery rows are found (including the case where the subquery returns no rows). The result is <SPAN CLASS="QUOTE" >"false"</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 <TT CLASS="TOKEN" >NOT IN</TT > 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 <TT CLASS="TOKEN" >EXISTS</TT >, it's unwise to assume that the subquery will be evaluated completely. </P ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > NOT IN (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The left-hand side of this form of <TT CLASS="TOKEN" >NOT IN</TT > is a row constructor, as described in <A HREF="sql-expressions.html#SQL-SYNTAX-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 <TT CLASS="TOKEN" >NOT IN</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if only unequal subquery rows are found (including the case where the subquery returns no rows). The result is <SPAN CLASS="QUOTE" >"false"</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 <TT CLASS="TOKEN" >NOT IN</TT > is null. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="FUNCTIONS-SUBQUERY-ANY-SOME" >9.22.4. <TT CLASS="LITERAL" >ANY</TT >/<TT CLASS="LITERAL" >SOME</TT ></A ></H2 ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >expression</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > ANY (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >) <TT CLASS="REPLACEABLE" ><I >expression</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > SOME (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</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 <TT CLASS="REPLACEABLE" ><I >operator</I ></TT >, which must yield a Boolean result. The result of <TT CLASS="TOKEN" >ANY</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if any true result is obtained. The result is <SPAN CLASS="QUOTE" >"false"</SPAN > if no true result is found (including the case where the subquery returns no rows). </P ><P > <TT CLASS="TOKEN" >SOME</TT > is a synonym for <TT CLASS="TOKEN" >ANY</TT >. <TT CLASS="TOKEN" >IN</TT > is equivalent to <TT CLASS="LITERAL" >= ANY</TT >. </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 <TT CLASS="TOKEN" >ANY</TT > 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 <TT CLASS="TOKEN" >EXISTS</TT >, it's unwise to assume that the subquery will be evaluated completely. </P ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > ANY (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >) <TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > SOME (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The left-hand side of this form of <TT CLASS="TOKEN" >ANY</TT > is a row constructor, as described in <A HREF="sql-expressions.html#SQL-SYNTAX-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 <TT CLASS="REPLACEABLE" ><I >operator</I ></TT >. The result of <TT CLASS="TOKEN" >ANY</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if the comparison returns true for any subquery row. The result is <SPAN CLASS="QUOTE" >"false"</SPAN > if the comparison returns false for every subquery row (including the case where the subquery returns no rows). The result is NULL if the comparison does not return true for any row, and it returns NULL for at least one row. </P ><P > See <A HREF="functions-comparisons.html#ROW-WISE-COMPARISON" >Section 9.23.5</A > for details about the meaning of a row-wise comparison. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="FUNCTIONS-SUBQUERY-ALL" >9.22.5. <TT CLASS="LITERAL" >ALL</TT ></A ></H2 ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >expression</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > ALL (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</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 <TT CLASS="REPLACEABLE" ><I >operator</I ></TT >, which must yield a Boolean result. The result of <TT CLASS="TOKEN" >ALL</TT > is <SPAN CLASS="QUOTE" >"true"</SPAN > if all rows yield true (including the case where the subquery returns no rows). The result is <SPAN CLASS="QUOTE" >"false"</SPAN > if any false result is found. The result is NULL if the comparison does not return false for any row, and it returns NULL for at least one row. </P ><P > <TT CLASS="TOKEN" >NOT IN</TT > is equivalent to <TT CLASS="LITERAL" ><> ALL</TT >. </P ><P > As with <TT CLASS="TOKEN" >EXISTS</TT >, it's unwise to assume that the subquery will be evaluated completely. </P ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > ALL (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The left-hand side of this form of <TT CLASS="TOKEN" >ALL</TT > is a row constructor, as described in <A HREF="sql-expressions.html#SQL-SYNTAX-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 <TT CLASS="REPLACEABLE" ><I >operator</I ></TT >. The result of <TT CLASS="TOKEN" >ALL</TT > is <SPAN CLASS="QUOTE" >"true"</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" >"false"</SPAN > if the comparison returns false for any subquery row. The result is NULL if the comparison does not return false for any subquery row, and it returns NULL for at least one row. </P ><P > See <A HREF="functions-comparisons.html#ROW-WISE-COMPARISON" >Section 9.23.5</A > for details about the meaning of a row-wise comparison. </P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN18263" >9.22.6. Row-wise Comparison</A ></H2 ><PRE CLASS="SYNOPSIS" ><TT CLASS="REPLACEABLE" ><I >row_constructor</I ></TT > <TT CLASS="REPLACEABLE" ><I >operator</I ></TT > (<TT CLASS="REPLACEABLE" ><I >subquery</I ></TT >)</PRE ><P > The left-hand side is a row constructor, as described in <A HREF="sql-expressions.html#SQL-SYNTAX-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 HREF="functions-comparisons.html#ROW-WISE-COMPARISON" >Section 9.23.5</A > for details about the meaning of a row-wise comparison. </P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="functions-window.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="functions-comparisons.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Window Functions</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="functions.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Row and Array Comparisons</TD ></TR ></TABLE ></DIV ></BODY ></HTML >