DROP FUNCTION name ( [ type [, ...] ] )
Use this parameter to provide the name of an existing function you wish to drop.
Use this parameter to specify the type of data the target function accepts as arguments.
Use this command to remove C function references that are defined in a database. Specifying the parameter types 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.
This command 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.