| The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group Paperback (6"x9"), 454 pages ISBN 9781906966041 RRP £14.95 ($19.95) Sales of this book support the PostgreSQL project! Get a printed copy>>> |
7.1 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 |
AND and OR are
commutative, that is, you can switch the left and right operand
without affecting the result. But see section 2.2.13 Expression Evaluation Rules for more information about the
order of evaluation of subexpressions.
| ISBN 9781906966041 | The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference | See the print edition |