and connects two expressions and returns results when both are true. or connects two or more conditions and returns results when either of the conditions is true.
When more than one logical operator is used in a statement, and is evaluated before or. You can change the order of execution with parentheses.
Table 4-6 shows the results of logical operations, including those that involve null values.
and |
TRUE |
FALSE |
NULL |
TRUE |
TRUE |
FALSE |
UNKNOWN |
FALSE |
FALSE |
FALSE |
FALSE |
NULL |
UNKNOWN |
FALSE |
UNKNOWN |
or |
TRUE |
FALSE |
NULL |
TRUE |
TRUE |
TRUE |
TRUE |
FALSE |
TRUE |
FALSE |
UNKNOWN |
NULL |
TRUE |
UNKNOWN |
UNKNOWN |
not |
|||
TRUE |
FALSE |
||
FALSE |
TRUE |
||
NULL |
UNKNOWN |
The result UNKNOWN indicates that one or more of the expressions evaluates to NULL, and that the result of the operation cannot be determined to be either TRUE or FALSE. See “Using nulls in expressions” for more information.
