Logic Operators

operator	description
AND	Logical AND
OR	Logical OR
NOT, !	Logical NOT

A logic operator returns a ternary value.

AND

condition AND condition

condition: value

If either of conditions is FALSE, then return FALSE. If both of conditions are not FALSE, and either of conditions is UNKNOWN, then return UNKNOWN. Otherwise, return TRUE.

OR

condition OR condition

condition: value

If either of conditions is TRUE, then return TRUE. If both of conditions are not TRUE, and either of conditions is UNKNOWN, then return UNKNOWN. Otherwise, return FALSE.

NOT

logical_not
  : NOT condition
  | !condition

condition: value

If the condition is TRUE, then return FALSE. If the condition is FALSE, then return TRUE. IF the condition is UNKNOWN, then return UNKNOWN.

NOT and ! return the same value, but there is the difference of precedence between these two operators.