Hello, Le 22/07/09 13:42, Frank Bax a écrit : > chester c young wrote: >>> Le 20/07/09 15:19, chester c young a écrit : >>>> within a trigger need to know if the UPDATE statement >>> set a column. the column might be set to the old value >>> or a different value. [...] >>>> >>> If the column to test is known -- e.g. column MyCol --, >>> NEW.MyCol and OLD.MyCol [...] can be compared. >> >> for example, >> create table t1( c1 int, c2 int ); >> insert into t1 values( 1, 2 ); >> >> 1) update t1 set c1=4 where c1=1; >> 2) update t1 set c1=4, c2=2 where c1=1; >> >> each update results in the same row, but in the second update c2 was >> actually set. >> a trigger on the update - how do we know if c2 has been actually set >> or not? > > You cannot do that. You can only detect that a value has changed. >
There would be one way to detect a value change but it is more related to application management than to data manipulation. For the column c2, it could be assumed that a flag is set when (a row of) c2 is updated. Such a flag may be stored in a separate table (while it could also be added to table t1) that is updated with a trigger based on update on t1. Regards. -- nha / Lyon / France. -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
