The following logical operators are available: AND
, OR
and NOT
. SQL uses a three-valuad logic system with TRUE
, FALSE
and NULL
. Note that logical operators involving NULL
do not always evaluate to NULL
. For example, NULL AND FALSE
will evaluate to FALSE
, and NULL OR TRUE
will evaluate to TRUE
. Below are the complete 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.