Logical Operators

The following logical operators are available: AND, OR and NOT. SQL uses a three-valued 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.

Binary Operators: AND and OR

Query

SELECT true AS "a", true AS "b", true AND true AS "a AND b", true OR true AS "a OR b"UNION ALL SELECT true, false, true AND false, true OR falseUNION ALL SELECT true, NULL, true AND NULL, true OR NULLUNION ALL SELECT false, false, false AND false, false OR falseUNION ALL SELECT false, NULL, false AND NULL, false OR NULLUNION ALL SELECT NULL, NULL, NULL AND NULL, NULL OR NULL;

Result

 a    | b    | a AND b | a OR b------+------+---------+-------- t    | t    | t       | t t    | f    | f       | t t    | NULL | NULL    | t f    | f    | f       | f f    | NULL | f       | NULL NULL | NULL | NULL    | NULL

Unary Operator: NOT

Query

SELECT true AS "a", NOT true AS "NOT a"UNION ALL SELECT false, NOT falseUNION ALL SELECT NULL, NOT NULL;

Result

 a    | NOT a------+------- t    | f f    | t NULL | NULL

The operators AND and OR are commutative, that is, you can switch the left and right operand without affecting the result.