PostgreSQL 8.2.12 Documentation
Prev | Fast Backward | Chapter 9. Functions and Operators | Fast Forward | Next

# 9.1. Logical Operators

The usual logical operators are available:

`AND`
`OR`
`NOT`

SQL uses a three-valued Boolean logic where the null value represents "unknown". Observe the following truth tables:

`a` | `b` | `a` AND `b` | `a` OR `b`
--- | --- | --- | ---
TRUE | TRUE | TRUE | TRUE
TRUE | FALSE | FALSE | TRUE
TRUE | NULL | NULL | TRUE
FALSE | FALSE | FALSE | FALSE
FALSE | NULL | FALSE | NULL
NULL | NULL | NULL | NULL

`a` | NOT `a`
--- | ---
TRUE | FALSE
FALSE | TRUE
NULL | NULL

The operators `AND` and `OR` are commutative, that is, you can switch the left and right operand without affecting the result. But see Section 4.2.12 for more information about the order of evaluation of subexpressions.

Prev | Home | Next
Functions and Operators | Up | Comparison Operators