Novel scenario of trigger mutation - take a look

Hi:

        It is the favorite mutation question of triggers. I know the cause of the error, only I cannot figure out why I am violating it!

        I have a before insert or update trigger that does a select on the same table on which the trigger is fired from. I thought that I cannot update/do some action that causes my trigger to fire again - trigger mutation is only caused by multiple firing of the same trigger. Will select on the same table (same row included  or not included) also cause mutation? I am baffled!

        I enclose the skeleton text of my trigger for further details:

	Create trigger Mytrigger 
		before insert or update of col1,col2, col3
		on mytable
		declare
			nMyValue	NUMBER;
	for each row
	BEGIN
		if :NEW.col1>0 then
			/* This fires and works great */
			update someothertable set col4=1
			where col2=:OLD.col2;
		elsif
			:NEW.col1=0 then


				/* This select mutates - Why? */


				select sum(col1) 
				into nMyValue
				from mytable
				where col2=:OLD.col2 and
				      col3 != :OLD.col3;


				/* I tried adding the second where


				clause to exclude the current row and
				hope the trigger would not mutate,
				but it still does! */
				if :nMyValue=0 then
					update someothertable set col4=0
					where col2=:OLD.col2;
				end if;
		end if;

	end;
	/

Please help,

thanks a lot,

-Badri Received on Sat Jan 13 1996 - 00:00:00 CET