8. Built-in Functions

Upgraders: PLEASE READ!

A large number of functions that were implemented as external functions (UDFs) in earlier versions of Firebird have been progressively re-implemented as internal (built-in) functions. If some external function of the same name as a built-in one is declared in your database, it will remain there and it will override any internal function of the same name.

To make the internal function available, you need either to DROP the UDF, or to use ALTER EXTERNAL FUNCTION to change the declared name of the UDF.