Update

I have the following situation: I have seen when tracing an application the following update statement(s), by example update table01 set (a, b) = ('xxx', 'yyyy') where a = 'xxx' On column a exists an unique index. I wondered why the application updates the column on which its selects. If I am not mistaken is updating the a column (very) bad for performance there the unique constraint has to verified, locks live longer, etc. My question is, is their more to tell about this kind of update, to help my to convince the designer to alter the update statements such as a higher chance on deadlocks, lock time-outs etc. The Informix version 7.20.UC2 Regards, Albert Wisse