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. 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:
SQL uses a three-valued Boolean logic where the null value represents
"unknown". Observe the following truth tables:
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 for more information about the
order of evaluation of subexpressions.