11th October 2018: PostgreSQL 11 RC 1 Released!

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.

`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

=`expression`

OR`value1`

=`expression`

OR ...`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.

```
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

<>`expression`

AND`value1`

<>`expression`

AND ...`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.

`x NOT IN y`

is equivalent to
`NOT (x IN y)`

in all cases. However,
null values are much more likely to trip up the novice when working
with `NOT IN`

than when working with
`IN`

. It is best to express your condition
positively if possible.

`ANY`

/`SOME`

(array)`expression`

ANY (`operator`

)`array expression`

`expression`

SOME (`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`

.

`ALL`

(array)`expression`

ALL (`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.

`row_constructor`

`operator`

`row_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.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.

Prior to PostgreSQL 8.2, the
`<`

, `<=`

, `>`

and
`>=`

cases were not handled per SQL
specification. A comparison like ```
ROW(a,b)
< ROW(c,d)
```

was implemented as ```
a
< c AND b < d
```

whereas the correct behavior is
equivalent to ```
a < c OR (a = c AND b <
d)
```

.

IS DISTINCT FROM`row_constructor`

`row_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 FROM`row_constructor`

`row_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.

`record`

`operator`

`record`

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.

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