External routines, the generic label used for UDFs, table UDFs, methods, and external procedures, are specific variations of one another and share most properties in common, including being written in a third-generation programming language such as C or C++.
See CREATE FUNCTION and REPLACE FUNCTION (External Form), CREATE FUNCTION (Table Form), and CREATE PROCEDURE and REPLACE PROCEDURE (External Form) for more information.
When an external routine is invoked, the system passes a handle to the UDT argument instead of the UDT value. Given the handle, an external routine can get, or set, the value of a UDT argument by means of a set of library functions provided by Teradata (see Teradata Vantage™ - SQL External Routine Programming, B035-1147).
The ANSI SQL standard contrasts external routines with what it refers to as SQL routines, which are routines written in the SQL language. The SQL form of procedures (see CREATE PROCEDURE and REPLACE PROCEDURE (SQL Form) is an example of an SQL routine.