Table of Contents
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 show the list of all actually
available functions and operators, respectively.
If you are concerned about portability then take 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 the 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 Boolean logic where the null value represents “unknown”. Observe the following truth tables:
a |
b |
a AND b
|
a OR b
|
---|---|---|---|
TRUE | TRUE | TRUE | TRUE |
TRUE | FALSE | FALSE | TRUE |
TRUE | NULL | NULL | TRUE |
FALSE | FALSE | FALSE | FALSE |
FALSE | NULL | FALSE | NULL |
NULL | NULL | NULL | NULL |
a |
NOT a
|
---|---|
TRUE | FALSE |
FALSE | TRUE |
NULL | NULL |
The operators AND
and OR
are
commutative, that is, you can switch the left and right operand
without affecting the result. But see Section 4.2.12, “Expression Evaluation Rules” for more information about the
order of evaluation of subexpressions.