If I create an ON UPDATE trigger run on each row after update, does
the trigger fire only on rows affected by the update or for all rows?
For example:
CREATE TRIGGER my_update_trigger
AFTER UPDATE ON my_table
FOR EACH ROW
EXECUTE PROCEDURE my_update_proc;
UPDATE my_table SET my_val = my_val * 2;
Will the trigger fire on rows that have NULL for my_val?
If so, would this be ok in the trigger proc to generically tell if
the row actually changed:
-- check if update affected the row
IF TG_OP = 'UPDATE' THEN
IF OLD = NEW THEN
RETURN NULL;
END IF;
END IF;
-- further processing here
Or would you have to compare each field in OLD, NEW to see if
anything actually changed?
Josh
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