Question

I love triggers for one reason – they just work. I hate triggers for one reason – when they don’t work, forget about trying to debug. O the sweet frustration.

Basically, I want to see THE update, delete, insert, etc query that was ran. I want to see that query … somewhere, in my terminal or a log, exactly how and when MySQL executes it, and possibly any corresponding output/errors. Thoughts/hacks?

I’m trying to debug an update query with a few joins and what not. My queries are much more complex but for brevity here’s an example.

DELIMITER |
CREATE TRIGGER ireallyhateyourightnow AFTER UPDATE ON watch_this_table
FOR EACH ROW BEGIN
 IF (OLD.my_value != NEW.my_value) THEN
  update 
   my_table
  set 
   my_column = NEW.my_value;
 END IF;
END|
DELIMITER ;

Here is some additional context that may help influence a suggestion or answer. Again, I’m less interested in semantics/syntax and more interested in seeing MySQL run the query but by all means, I’m open to anything at this point.

• Strace does not work/show query.
• Non-replicated environment BUT if the bin logs show trigger statements I will certainly set this up.
• Does “show full processlist” show trigger execution and/or statements executed within (I never see them after running show full processlist as fast as perl can run it but I might just be missing it)?
• General query log does not show these queries (certainly not the error log).
• I’m not using aliases (anymore).
• No syntax errors when creating the trigger.
• The IF statement works.
• When I insert the NEW values into a “test/temp” table and manually run the update query it works (I’ve even went so far as to actually inserting the whole update query)
• I can’t show you the query but as I just mentioned, it works when I run manually if that helps.
• I’ve removed all erroneous characters, tabs, carriage returns, newlines, etc.
• The MySQL socket would only show local connection/data but not MySQL internal workings, I think.
• MyISAM so INNODB logs aren’t an option
• lsof didn’t seem to show anything else to be of use.
• I’m using MySQL 5.0.77 on CentOS 5.5.

Answer 1

You can debug triggers using dbForge Studio for MySQL. Try trial version.

There is a detailed description of the trigger debugging process in the documentation: Debugging \ Debugging Stored Routines \ How To: Start Trigger Debugging.