I just found something, don't know if it's correct. Will this work following my UPDATE?

exec sql

get diagnostics :rcount = row_count;

In Theory, the row count is returned by the diagnostics statement that you found, but in general, the number of rows updated is returned to the SQLERR array as the first two bytes (as an integer). Do the UPDATE, then look at the SQLERR in debug, as follows:

EVAL  SQLERR:X

And see if it looks like the correct number of rows.

Will do. Thanks, Bob!

That's it. ROW_COUNT is updated by UPDATE, DELETE, and INSERT. It's in Diagnostics Area (see GET DIAGNOSTICS), or SQLERRD(3) in the SQLCA. ROW_COUNT is just the UPDATE itself; it does not include other rows affected by triggers or referential constraints. If you want the secondary rows affected, then DB2_ROW_COUNT_SECONDARY, which is SQLERRD(5).

If you're embedding it in RPG, The SQLCA is declared automatically, and RPG does the GET DIAGNOSTICS for you. You just need to access the appropriate field.

The SQLCA has an OVERLAY. SQLERRD() array is 10I 0. It OVERLAYs SQLER3 and SQLER5 (etc.), which are 9B0. I'd go with the SQLERRD(), just because I prefer the integer over the older binary.

Exec SQL UPDATE mylib.mytable
           SET field1 = field1 + 1
           WHERE field2 = 'x';
rcount = SQLERRD(3);

Note that the assignment of rcount from SQLERRD(3) is a normal RPG statement, not an Exec-SQL.