MYSQL Error - How can I log the Query (not only _error_messge())

[eluser]ladooboy[/eluser]
Thanks for the info. This was already enabled, but I just needed to log the query for error purposes later in live.

PS: I am a little confused with mysql errors. When a user is trying to log in and all the insert/update etc. commands are executed. Some of them might fail for what ever reason, should I show this as a fatal error with show_error() and terminate the application or should I just log the error, but that means checking the success of EVERY query. Is this practical ?

But then if lets say the session table wasn't updated properly or the user tables, this is a really major problem. Is it better to terminate the application in this instance ?

I am currently trying to implement some DB exception etc. and I am really confused how to do the design and when exactly to call what errors.