About

User-defined Functions (UDFs) is a function provided by a developer and behave as a built-in function. It gives to the developer the possibility to enhance the function possibilities of an application (generally a query language).

Example

For a database:

SELECT myfunc(r.a, r.b)
WHERE yourfunc(r.c, r.d) < 5
SELECT x, concat(r.s) M
GROUP BY x
SELECT W FROM tablefunc(a,b)