# Row and Array Comparisons

PostgreSQL 9.5.3 Documentation | |||
---|---|---|---|

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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 PostgreSQL extensions; the rest are SQL -compliant. All of the expression forms documented in this section return Boolean (true/false) results.

##
9.23.1.
`
IN
`

IN (expression[, ...])value

The right-hand side is a parenthesized list of scalar expressions. The result is "true" if the left-hand expression's result is equal to any of the right-hand expressions. This is a shorthand notation for

=expressionORvalue1=expressionOR ...value2

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
`
IN
`
construct will be null, not false.
This is in accordance with SQL's normal rules for Boolean combinations
of null values.

##
9.23.2.
`
NOT IN
`

NOT IN (expression[, ...])value

The right-hand side is a parenthesized list of scalar expressions. The result is "true" if the left-hand expression's result is unequal to all of the right-hand expressions. This is a shorthand notation for

<>expressionANDvalue1<>expressionAND ...value2

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
`
NOT IN
`
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.

Tip:x NOT IN yis equivalent toNOT (x IN y)in all cases. However, null values are much more likely to trip up the novice when working withNOT INthan when working withIN. It is best to express your condition positively if possible.

##
9.23.3.
`
ANY
`
/
`
SOME
`
(array)

expressionANY (operator)array expressionexpressionSOME (operator)array expression

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
`
operator
`
, which must yield a Boolean
result.
The result of

`ANY`is "true" if any true result is obtained. The result is "false" if no true result is found (including the case where the array has zero elements).

If the array expression yields a null array, the result of
`
ANY
`
will be null. If the left-hand expression yields null,
the result of
`
ANY
`
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
`
ANY
`
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.

`
SOME
`
is a synonym for
`
ANY
`
.

##
9.23.4.
`
ALL
`
(array)

expressionALL (operator)array expression

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
`
operator
`
, which must yield a Boolean
result.
The result of

`ALL`is "true" if all comparisons yield true (including the case where the array has zero elements). The result is "false" if any false result is found.

If the array expression yields a null array, the result of
`
ALL
`
will be null. If the left-hand expression yields null,
the result of
`
ALL
`
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
`
ALL
`
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.

## 9.23.5. Row Constructor Comparison

row_constructoroperatorrow_constructor

Each side is a row constructor,
as described in
Section 4.2.13
.
The two row values must have the same number of fields.
Each side is evaluated and they are compared row-wise. Row constructor
comparisons are allowed when the
`
operator
`
is

`=`,

`<>`,

`<`,

`<=`,

`>`or

`>=`. Every row element must be of a type which has a default B-tree operator class or the attempted comparison may generate an error.

Note:Errors related to the number or types of elements might not occur if the comparison is resolved using earlier columns.

The
`
=
`
and
`
<>
`
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).

For the
`
<
`
,
`
<=
`
,
`
>
`
and
`
>=
`
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,
`
ROW(1,2,NULL) < ROW(1,3,0)
`
yields true, not null, because the third pair of elements are not
considered.

Note:Prior to PostgreSQL 8.2, the<,<=,>and>=cases were not handled per SQL specification. A comparison likeROW(a,b) < ROW(c,d)was implemented asa < c AND b < dwhereas the correct behavior is equivalent toa < c OR (a = c AND b < d).

IS DISTINCT FROMrow_constructorrow_constructor

This construct is similar to a
`
<>
`
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.

IS NOT DISTINCT FROMrow_constructorrow_constructor

This construct is similar to a
`
=
`
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.

## 9.23.6. Composite Type Comparison

recordoperatorrecord

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. PostgreSQL does this only when comparing the results of two row constructors (as in Section 9.23.5 ) or comparing a row constructor to the output of a subquery (as in Section 9.22 ). 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.

Each side is evaluated and they are compared row-wise. Composite type
comparisons are allowed when the
`
operator
`
is

`=`,

`<>`,

`<`,

`<=`,

`>`or

`>=`, 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

`=`member of a B-tree operator class.) The default behavior of the above operators is the same as for

`IS [ NOT ] DISTINCT FROM`for row constructors (see Section 9.23.5 ).

To support matching of rows which include elements without a default
B-tree operator class, the following operators are defined for composite
type comparison:
`
*=
`
,
`
*<>
`
,
`
*<
`
,
`
*<=
`
,
`
*>
`
, and
`
*>=
`
.
These operators compare the internal binary representation of the two
rows. Two rows might have a different binary representation even
though comparisons of the two rows with the equality operator is true.
The ordering of rows under these comparison operators is deterministic
but not otherwise meaningful. These operators are used internally for
materialized views and might be useful for other specialized purposes
such as replication but are not intended to be generally useful for
writing queries.