Create a standard UDF in three steps, two of which are optional:
When an SQL query calls a UDF, the
init routine for that function is called first, if
it exists. This routine is responsible for allocating data and
setting certain parameters for the
is called, the
main routine for the desired UDF is
called. This is the only routine required to exist to define a UDF.
This routine is responsible for processing the data and returning the
result of the function.
is finished and the result is returned to the user, MySQL will call a
deinit routine for the function, if it exists. The
purpose of this routine is to deallocate any memory allocated by the
init routine and clean up as necessary.
When an SQL query calls a standard function, these routines are called in the following manner:
init main main main ... deinit
MySQL calls the
main routine once for each row
returned by the SQL query. The return values of the
main routine comprise the results of the UDF as a
When creating a UDF, all three routines must reside in the same library. You can, however, bundle multiple functions in the same library.
We use the terms "routine" and "function" in a specific manner in this section to reduce the possibility of confusion. The problem is that multiple native functions make up a single UDF. When we refer to a routine, we mean one of the native functions that make up the UDF. When we refer ...