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Syntax
[ AND | OR | NOT ]
Semantics
SQL uses a three-valued Boolean logic where the null value represents "unknown."
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 |
Notes
AND and OR are commutative, that is, you can switch the left and right operand without affecting the result. However, the order of evaluation of subexpressions is not defined. When it is essential to force evaluation order, use a CASE construct.