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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-COMPARISONS"
>9.23. Row and Array Comparisons</A
></H1
><P
> This section describes several specialized constructs for making
multiple comparisons between groups of values. These forms are
syntactically related to the subquery forms of the previous section,
but do not involve subqueries.
The forms involving array subexpressions are
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extensions; the rest are
<ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>-compliant.
All of the expression forms documented in this section return
Boolean (true/false) results.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN18300"
>9.23.1. <TT
CLASS="LITERAL"
>IN</TT
></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 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>
</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 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
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN18316"
>9.23.2. <TT
CLASS="LITERAL"
>NOT IN</TT
></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 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>
</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 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 is best to express your condition positively if possible.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN18338"
>9.23.3. <TT
CLASS="LITERAL"
>ANY</TT
>/<TT
CLASS="LITERAL"
>SOME</TT
> (array)</A
></H2
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> ANY (<TT
CLASS="REPLACEABLE"
><I
>array expression</I
></TT
>)
<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> SOME (<TT
CLASS="REPLACEABLE"
><I
>array expression</I
></TT
>)</PRE
><P
> The right-hand side is a parenthesized expression, which must yield an
array value.
The left-hand expression
is evaluated and compared to each element of the array 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 array has zero elements).
</P
><P
> If the array expression yields a null array, the result of
<TT
CLASS="TOKEN"
>ANY</TT
> will be null. If the left-hand expression yields null,
the result of <TT
CLASS="TOKEN"
>ANY</TT
> is ordinarily null (though a non-strict
comparison operator could possibly yield a different result).
Also, if the right-hand array contains any null elements and no true
comparison result is obtained, the result of <TT
CLASS="TOKEN"
>ANY</TT
>
will be null, not false (again, assuming a strict comparison operator).
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</P
><P
> <TT
CLASS="TOKEN"
>SOME</TT
> is a synonym for <TT
CLASS="TOKEN"
>ANY</TT
>.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN18361"
>9.23.4. <TT
CLASS="LITERAL"
>ALL</TT
> (array)</A
></H2
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> ALL (<TT
CLASS="REPLACEABLE"
><I
>array expression</I
></TT
>)</PRE
><P
> The right-hand side is a parenthesized expression, which must yield an
array value.
The left-hand expression
is evaluated and compared to each element of the array 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 comparisons yield true
(including the case where the array has zero elements).
The result is <SPAN
CLASS="QUOTE"
>"false"</SPAN
> if any false result is found.
</P
><P
> If the array expression yields a null array, the result of
<TT
CLASS="TOKEN"
>ALL</TT
> will be null. If the left-hand expression yields null,
the result of <TT
CLASS="TOKEN"
>ALL</TT
> is ordinarily null (though a non-strict
comparison operator could possibly yield a different result).
Also, if the right-hand array contains any null elements and no false
comparison result is obtained, the result of <TT
CLASS="TOKEN"
>ALL</TT
>
will be null, not true (again, assuming a strict comparison operator).
This is in accordance with SQL's normal rules for Boolean combinations
of null values.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="ROW-WISE-COMPARISON"
>9.23.5. 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
>row_constructor</I
></TT
></PRE
><P
> Each side is a row constructor,
as described in <A
HREF="sql-expressions.html#SQL-SYNTAX-ROW-CONSTRUCTORS"
>Section 4.2.13</A
>.
The two row values must have the same number of fields.
Each side is evaluated and they are compared row-wise. Row comparisons
are allowed when the <TT
CLASS="REPLACEABLE"
><I
>operator</I
></TT
> is
<TT
CLASS="LITERAL"
>=</TT
>,
<TT
CLASS="LITERAL"
><></TT
>,
<TT
CLASS="LITERAL"
><</TT
>,
<TT
CLASS="LITERAL"
><=</TT
>,
<TT
CLASS="LITERAL"
>></TT
> or
<TT
CLASS="LITERAL"
>>=</TT
>,
or has semantics similar to one of these. (To be specific, an operator
can be a row comparison operator if it is a member of a B-tree operator
class, or is the negator of the <TT
CLASS="LITERAL"
>=</TT
> member of a B-tree operator
class.)
</P
><P
> The <TT
CLASS="LITERAL"
>=</TT
> and <TT
CLASS="LITERAL"
><></TT
> cases work slightly differently
from the others. 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
><P
> For the <TT
CLASS="LITERAL"
><</TT
>, <TT
CLASS="LITERAL"
><=</TT
>, <TT
CLASS="LITERAL"
>></TT
> and
<TT
CLASS="LITERAL"
>>=</TT
> cases, the row elements are compared left-to-right,
stopping as soon as an unequal or null pair of elements is found.
If either of this pair of elements is null, the result of the
row comparison is unknown (null); otherwise comparison of this pair
of elements determines the result. For example,
<TT
CLASS="LITERAL"
>ROW(1,2,NULL) < ROW(1,3,0)</TT
>
yields true, not null, because the third pair of elements are not
considered.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Prior to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.2, the
<TT
CLASS="LITERAL"
><</TT
>, <TT
CLASS="LITERAL"
><=</TT
>, <TT
CLASS="LITERAL"
>></TT
> and <TT
CLASS="LITERAL"
>>=</TT
>
cases were not handled per SQL specification. A comparison like
<TT
CLASS="LITERAL"
>ROW(a,b) < ROW(c,d)</TT
>
was implemented as
<TT
CLASS="LITERAL"
>a < c AND b < d</TT
>
whereas the correct behavior is equivalent to
<TT
CLASS="LITERAL"
>a < c OR (a = c AND b < d)</TT
>.
</P
></BLOCKQUOTE
></DIV
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>row_constructor</I
></TT
> IS DISTINCT FROM <TT
CLASS="REPLACEABLE"
><I
>row_constructor</I
></TT
></PRE
><P
> This construct is similar to a <TT
CLASS="LITERAL"
><></TT
> row comparison,
but it does not yield null for null inputs. Instead, any null value is
considered unequal to (distinct from) any non-null value, and any two
nulls are considered equal (not distinct). Thus the result will
either be true or false, never null.
</P
><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>row_constructor</I
></TT
> IS NOT DISTINCT FROM <TT
CLASS="REPLACEABLE"
><I
>row_constructor</I
></TT
></PRE
><P
> This construct is similar to a <TT
CLASS="LITERAL"
>=</TT
> row comparison,
but it does not yield null for null inputs. Instead, any null value is
considered unequal to (distinct from) any non-null value, and any two
nulls are considered equal (not distinct). Thus the result will always
be either true or false, never null.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> The SQL specification requires row-wise comparison to return NULL if the
result depends on comparing two NULL values or a NULL and a non-NULL.
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does this only when comparing the
results of two row constructors or comparing a row constructor to the
output of a subquery (as in <A
HREF="functions-subquery.html"
>Section 9.22</A
>).
In other contexts where two composite-type values are compared, two
NULL field values are considered equal, and a NULL is considered larger
than a non-NULL. This is necessary in order to have consistent sorting
and indexing behavior for composite types.
</P
></BLOCKQUOTE
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