9.1. Logical Operators
The usual logical operators are available:
AND |
OR |
NOT |
SQL uses a three-valued logic system with true, false, and The operatorsnull, which represents“unknown”. Observe the following truth tables:aba ANDba ORbTRUE TRUE TRUE TRUE TRUE FALSE FALSE TRUE TRUE NULL NULL TRUE FALSE FALSE FALSE FALSE FALSE NULL FALSE NULL NULL NULL NULL NULL aNOT aTRUE FALSE FALSE TRUE NULL NULL AND andOR are commutative, that is, you can switch the left and right operand without affecting the result. But seeSection 4.2.14 for more information about the order of evaluation of subexpressions.