Chapter 9. Functions and Operators

PostgreSQL™ provides a large number of functions and operators for the built-in data types. Users can also define their own functions and operators, as described in Part V, “Server Programming”. The psql commands \df and \do can be used to list all available functions and operators, respectively.

If you are concerned about portability then note that most of the functions and operators described in this chapter, with the exception of the most trivial arithmetic and comparison operators and some explicitly marked functions, are not specified by the SQL standard. Some of this extended functionality is present in other SQL database management systems, and in many cases this functionality is compatible and consistent between the various implementations. This chapter is also not exhaustive; additional functions appear in relevant sections of the manual.

The usual logical operators are available:

AND
OR
NOT

SQL uses a three-valued logic system with true, false, and null, which represents unknown. Observe the following truth tables:

aba AND ba OR b
TRUETRUETRUETRUE
TRUEFALSEFALSETRUE
TRUENULLNULLTRUE
FALSEFALSEFALSEFALSE
FALSENULLFALSENULL
NULLNULLNULLNULL

aNOT a
TRUEFALSE
FALSETRUE
NULLNULL

The operators AND and OR are commutative, that is, you can switch the left and right operand without affecting the result. But see the section called “Expression Evaluation Rules” for more information about the order of evaluation of subexpressions.