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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-SUBQUERY"
>9.20. Subquery Expressions</A
></H1
><A
NAME="AEN16334"
></A
><A
NAME="AEN16336"
></A
><A
NAME="AEN16338"
></A
><A
NAME="AEN16340"
></A
><A
NAME="AEN16342"
></A
><A
NAME="AEN16344"
></A
><A
NAME="AEN16346"
></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"
><H2
CLASS="SECT2"
><A
NAME="AEN16351"
>9.20.1. <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="AEN16375"
>9.20.2. <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 4.2.12</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="AEN16400"
>9.20.3. <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 4.2.12</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="AEN16425"
>9.20.4. <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 4.2.12</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 9.21.5</A
> for details about the meaning
   of a row-wise comparison.
  </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN16466"
>9.20.5. <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"
>&lt;&gt; 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 4.2.12</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 9.21.5</A
> for details about the meaning
   of a row-wise comparison.
  </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN16496"
>9.20.6. Row-wise Comparison</A
></H2
><A
NAME="AEN16498"
></A
><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 4.2.12</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 9.21.5</A
> for details about the meaning
   of a row-wise comparison.
  </P
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