Re: Update Trigger in IDS 7.3

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