PostgreSQL 7.4 Documentation | ||||
---|---|---|---|---|

Prev | Fast Backward | Chapter 9. Functions and Operators | Fast Forward | Next |

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.

expressionIN (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=value1ORexpression=value2OR ...

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.

expressionNOT IN (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<>value1ANDexpression<>value2AND ...

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's best to express your condition positively if possible.

expressionoperatorANY (array expression)expressionoperatorSOME (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 special
case where the array has zero elements).

`SOME` is a synonym for `ANY`.

expressionoperatorALL (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 special case where the array has zero elements).
The result is "false" if any false result is found.

(expression[,expression...])operator(expression[,expression...])

Each side is a list of scalar expressions; the two lists must be
of the same length. Each side is evaluated and they are compared
row-wise.
Presently, only `=` and `<>` operators are allowed
in row-wise comparisons.
The result is "true" if the two rows are equal or unequal, respectively.

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 the row comparison is unknown (null).