Re: Update Trigger in IDS 7.3

Stefan Weideneder wrote: > > Madan Mashalkar wrote: > > > > Hi, > > > > Environment : IDS 7.30UC3 , Sun Solaris > > This is a question about update triggers. > > > > There is a simple trigger: > > create trigger upd_tab1 update of col2 on tab1 > > referencing old as pre new as post> > > > (insert into tab2 (col1,col2) values ('GOT' ,'IT!' )); > > > > Then inserting and updating a row in an empty table tab1: > > > > insert into tab1 (col1,col2) values('TEST',null); > > update tab1 set col2 = 'NEW' where col1 = 'TEST';> > > > No rows are inserted in tab2. > > (Interesting, if either the pre or the post value is NULL, > > no rows are inserted in tab2) > > > > The manual states that if the 'when' evaluates to false/unknown, then > > the action(insert) will not be done. > > > > So, does (pre.col2 != post.col2) evaluate to unknown ??? > > If yes, then is it expected behaviour ? > > > > Confused , and awaiting clarifications... > > > > Thanks > > Madan > > Hi, > > never try to compare NULL values by equal (=) or not-equal (!=) > operators. Expand your condition to: > > for each row when (pre.col2 != post.col2 or pre.col2 is null > or post.col2 is null ) > > Because (NULL = NULL) will be evaluated to FALSE. > > Bye > > Stefan Weideneder Forget my stupid expansion. I hope you know what I was trying to say. ( I'll visit my bedroom now ! ) Bye Stefan Weideneder