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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-SUBQUERY"
>6.15. Subquery Expressions</A
></H1
><A
NAME="AEN10465"
></A
><A
NAME="AEN10467"
></A
><A
NAME="AEN10469"
></A
><A
NAME="AEN10471"
></A
><A
NAME="AEN10473"
></A
><A
NAME="AEN10475"
></A
><A
NAME="AEN10477"
></A
><P
> This section describes the <SPAN
CLASS="ACRONYM"
>SQL</SPAN
>-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="AEN10482"
>6.15.1. EXISTS</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 far 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 any side effects (such as
calling sequence functions); whether the side effects occur or not
may be difficult to predict.
</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 uninteresting. 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 multiple 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="AEN10505"
>6.15.2. IN (scalar form)</A
></H2
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> IN (<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>[<SPAN
CLASS="OPTIONAL"
>, ...</SPAN
>])</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>IN</TT
> is a parenthesized list
of scalar expressions. The result is <SPAN
CLASS="QUOTE"
>"true"</SPAN
> if the left-hand expression's
result is equal to any of the right-hand expressions. This is a shorthand
notation for
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>value1</I
></TT
>
OR
<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> = <TT
CLASS="REPLACEABLE"
><I
>value2</I
></TT
>
OR
...</PRE
><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 expression 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
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> This form of <TT
CLASS="TOKEN"
>IN</TT
> is not truly a subquery expression, but it
seems best to document it in the same place as subquery <TT
CLASS="TOKEN"
>IN</TT
>.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN10524"
>6.15.3. IN (subquery form)</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 of this form of <TT
CLASS="TOKEN"
>IN</TT
> 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 special
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
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) IN (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>IN</TT
> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. 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 special
case where the subquery returns no rows).
</P
><P
> As usual, null values in the expressions or subquery 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 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="AEN10550"
>6.15.4. NOT IN (scalar form)</A
></H2
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> NOT IN (<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>[<SPAN
CLASS="OPTIONAL"
>, ...</SPAN
>])</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>NOT IN</TT
> is a parenthesized list
of scalar expressions. The result is <SPAN
CLASS="QUOTE"
>"true"</SPAN
> if the left-hand expression's
result is unequal to all of the right-hand expressions. This is a shorthand
notation for
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> <> <TT
CLASS="REPLACEABLE"
><I
>value1</I
></TT
>
AND
<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> <> <TT
CLASS="REPLACEABLE"
><I
>value2</I
></TT
>
AND
...</PRE
><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 expression yields
null, the result of the <TT
CLASS="TOKEN"
>NOT IN</TT
> construct will be null, not true
as one might naively expect.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
> <TT
CLASS="LITERAL"
>x NOT IN y</TT
> is equivalent to <TT
CLASS="LITERAL"
>NOT (x IN y)</TT
> in all
cases. However, null values are much more likely to trip up the novice when
working with <TT
CLASS="TOKEN"
>NOT IN</TT
> than when working with <TT
CLASS="TOKEN"
>IN</TT
>.
It's best to express your condition positively if possible.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN10571"
>6.15.5. NOT IN (subquery form)</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 of this form of <TT
CLASS="TOKEN"
>NOT IN</TT
> 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 special 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
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) NOT IN (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>NOT IN</TT
> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. 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 special 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 expressions or subquery 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 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="AEN10597"
>6.15.6. ANY/SOME</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 of this form of <TT
CLASS="TOKEN"
>ANY</TT
> 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 special
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
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> ANY (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)
(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> SOME (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>ANY</TT
> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. 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
>. Presently,
only <TT
CLASS="LITERAL"
>=</TT
> and <TT
CLASS="LITERAL"
><></TT
> operators are allowed
in row-wise <TT
CLASS="TOKEN"
>ANY</TT
> queries.
The result of <TT
CLASS="TOKEN"
>ANY</TT
> is <SPAN
CLASS="QUOTE"
>"true"</SPAN
> if any equal or unequal row is
found, respectively.
The result is <SPAN
CLASS="QUOTE"
>"false"</SPAN
> if no such row is found (including the special
case where the subquery returns no rows).
</P
><P
> As usual, null values in the expressions or subquery 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 there is at least one null row result, then the result of <TT
CLASS="TOKEN"
>ANY</TT
>
cannot be false; it will be true or null.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN10643"
>6.15.7. ALL</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 of this form of <TT
CLASS="TOKEN"
>ALL</TT
> 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 special case where the subquery returns no rows).
The result is <SPAN
CLASS="QUOTE"
>"false"</SPAN
> if any false result is found.
</P
><P
> <TT
CLASS="TOKEN"
>NOT IN</TT
> is equivalent to <TT
CLASS="LITERAL"
><> ALL</TT
>.
</P
><P
> Note that if there are no failures but at least one right-hand row yields
null for the operator's result, the result of the <TT
CLASS="TOKEN"
>ALL</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
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> ALL (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)
</PRE
><P
> The right-hand side of this form of <TT
CLASS="TOKEN"
>ALL</TT
> is a parenthesized
subquery, which must return exactly as many columns as there are
expressions in the left-hand list. 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
>. Presently,
only <TT
CLASS="LITERAL"
>=</TT
> and <TT
CLASS="LITERAL"
><></TT
> operators are allowed
in row-wise <TT
CLASS="TOKEN"
>ALL</TT
> queries.
The result of <TT
CLASS="TOKEN"
>ALL</TT
> is <SPAN
CLASS="QUOTE"
>"true"</SPAN
> if all subquery rows are equal
or unequal, respectively (including the special
case where the subquery returns no rows).
The result is <SPAN
CLASS="QUOTE"
>"false"</SPAN
> if any row is found to be unequal or equal,
respectively.
</P
><P
> As usual, null values in the expressions or subquery 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 there is at least one null row result, then the result of <TT
CLASS="TOKEN"
>ALL</TT
>
cannot be true; it will be false or null.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN10679"
>6.15.8. Row-wise Comparison</A
></H2
><PRE
CLASS="SYNOPSIS"
>(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>subquery</I
></TT
>)
(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>]) <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> (<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> [<SPAN
CLASS="OPTIONAL"
>, <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> ...</SPAN
>])
</PRE
><P
> The left-hand side is a list of scalar expressions. The right-hand side
can be either a list of scalar expressions of the same length, or a
parenthesized subquery, which must return exactly as many columns as there
are expressions on the left-hand side. 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, or to the right-hand expression list.
Presently, only <TT
CLASS="LITERAL"
>=</TT
> and <TT
CLASS="LITERAL"
><></TT
> operators are allowed
in row-wise comparisons.
The result is <SPAN
CLASS="QUOTE"
>"true"</SPAN
> if the two rows are equal or unequal, respectively.
</P
><P
> As usual, null values in the expressions or subquery 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 the row comparison is unknown (null).
</P
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