PostgreSQL Essential Reference

Logical Operators

The logical operators usually are used to combine expressions to get an aggregate Boolean value from the list.

Listing

AND	Functions as a logical AND criteria connector.
OR	Functions as a logical OR criteria connector.
NOT	Functions as a negator.

Notes/Examples

SELECT * FROM payroll WHERE firstname="Bill" AND lastname="Smith"; 
SELECT * FROM payroll WHERE firstname="Bill" OR firstname="Sam"; 
SELECT * FROM payroll WHERE firstname IS NOT NULL;