DROP FUNCTION name ( [ type [, ...] ] )
The name of the existing function you wish to drop.
Zero or more data types consisting of the function's arguments. The types combine with the name to uniquely identify the function.
Use this command to remove C function references that are defined in a database. Specifying the parameter types that the function takes allows proper identification; this is necessary when dealing with the C language, as functions exist with the same name that only differ in the types of arguments they take.
DROP FUNCTION does not check if any database elements rely on the function, or if removing it would cause any negative effects. You must check these things on your own.
The following example removes the title(integer) function from the booktown database:
booktown=# DROP FUNCTION title(integer); DROP