38.9. Internal Functions
Internal functions are functions written in C that have been statically linked into the PostgreSQL server. The " body " of the function definition specifies the C-language name of the function, which need not be the same as the name being declared for SQL use. (For reasons of backward compatibility, an empty body is accepted as meaning that the C-language function name is the same as the SQL name.)
Normally, all internal functions present in the
server are declared during the initialization of the database cluster
(see
Section 19.2
),
but a user could use
CREATE FUNCTION
to create additional alias names for an internal function.
Internal functions are declared in
CREATE FUNCTION
with language name
internal
. For instance, to
create an alias for the
sqrt
function:
CREATE FUNCTION square_root(double precision) RETURNS double precision
AS 'dsqrt'
LANGUAGE internal
STRICT;
(Most internal functions expect to be declared " strict " .)
Note
Not all " predefined " functions are " internal " in the above sense. Some predefined functions are written in SQL.