Example: Counter

Suppose you want to number the rows in your SELECT statement. So you write a UDF which increments and returns a counter.

Note: By using the code examples, you agree to the terms of the Code license and disclaimer information.

This example uses an external function with DB2^® SQL parameter style and a scratchpad.

CREATE FUNCTION COUNTER()
       RETURNS INT
       SCRATCHPAD
       NOT DETERMINISTIC
       NO SQL
       NO EXTERNAL ACTION
       LANGUAGE C
       PARAMETER STYLE DB2SQL
       EXTERNAL NAME 'MYLIB/MATH(ctr)'
       DISALLOW PARALLEL

/* structure scr defines the passed scratchpad for the function "ctr" */
struct scr {
   long len;
   long countr;
   char not_used[96];
};

void ctr (
   long *out,                           /* output answer (counter) */
   short *outnull,                      /* output NULL indicator */
   char *sqlstate,                      /* SQL STATE */
   char *funcname,                      /* function name */
   char *specname,                      /* specific function name */
   char *mesgtext,                      /* message text insert */
   struct scr *scratchptr) {            /* scratch pad */

   *out = ++scratchptr->countr;      /* increment counter & copy out */
   *outnull = 0;
   return;
}
/* end of UDF : ctr */

For this UDF, observe that:

It has no input SQL arguments defined, but returns a value.
It appends the scratchpad input argument after the four standard trailing arguments, namely SQL-state, function-name, specific-name, and message-text.
It includes a structure definition to map the scratchpad which is passed.
No input parameters are defined. This agrees with the code.
SCRATCHPAD is coded, causing DB2 to allocate, properly initialize and pass the scratchpad argument.
You have specified it to be NOT DETERMINISTIC, because it depends on more than the SQL input arguments, (none in this case).
You have correctly specified DISALLOW PARALLEL, because correct functioning of the UDF depends on a single scratchpad.