Comments on: How To Use Triggers to Track Changes in MySQL

By: Ali

Ali — Sat, 01 May 2010 16:37:18 +0000

great to have found this site. I have used all search engines to find someone trying to update a table based on input changes. My issue was:
1- keep loading a table everyday.
2- data rows that is to load the table are repetitive. Not all of them change in value
3- once i use insert .... on duplicate key update . The table updates with the new information irrespective whether the values are equal or not. I am not sure why, but I have a timestamp field among the fields. And, i am passing a current_timestamp() function in the insert statement. This is needed to timestamp new records, and timestamp the duplicate key records if any of their values differ.
What I ended up getting, an updated timestamp that is always current. I lose track whether a real change exist in the values themselves. I think timestamp fields update with a timestamp irrespective whether other values change, that's because the timestamp field by itself changed. Enough to execute the update. This is the first caveat. What I really want is to leave the row unchanged based on the values i am checking and reset the timestamp to the old one.
so, the trigger helped me achieve that by putting an if then else statement. Similar to the above, yet introduced the else and SET new.timestamp = old.timestamp, new.counter=old.counter. My if checks all the values that might have changes with
IF NEW.VALUE<>OLD.VALUE OR NEW.VALUE_1 <> OLD.VALUE_1 for all values ...,
THEN INSERT INTO history_table SELECT * FROM table WHERE identifiers are =..
(The OLD.* didn't work.)
ELSE SET NEW.TIMESTAMP=OLD.TIMESTAMP, NEW.COUNTER=OLD.COUNTER

That did the magic, because it neutralized the new buffer to the old buffer and the update needn't to execute.

Hope that helps those who have the same issue.

By: Anthony

Anthony — Fri, 22 Jan 2010 10:58:24 +0000

perfect… exactly what I was looking for.

By: Phani Kumar Varanasi

Phani Kumar Varanasi — Thu, 12 Nov 2009 04:24:16 +0000

Yeah Dear, the concept you entered is so helpful, well good work.

By: abhinavzone

abhinavzone — Wed, 29 Jul 2009 16:57:23 +0000

Thank you very much!!! it saved my day

By: Mysql Trigger Tutorial and Tools | Learning On Demand

Mysql Trigger Tutorial and Tools | Learning On Demand — Thu, 18 Jun 2009 15:50:50 +0000

[...] How To Use Triggers to Track Changes in MySQL, more advance sample. [...]

By: Greg Allard

Greg Allard — Mon, 20 Apr 2009 16:18:54 +0000

I don't think there is anyway to do it in the database, but you can still put the logic in your application. If you are using django, there are signals that will help get that done. http://docs.djangoproject.com/en/1.0/topics/sig... If you aren't then you will need to program it into your project in some other way.

By: Sean

Sean — Mon, 20 Apr 2009 16:03:18 +0000

Does any way work as trigger in mysql 4.1? I know that triggers is supported from mysql 5.0
thanks for help

By: IT Tutorials » Mysql Trigger Tutorial and Tools

IT Tutorials » Mysql Trigger Tutorial and Tools — Mon, 16 Mar 2009 09:48:06 +0000

[...] How To Use Triggers to Track Changes in MySQL, more advance sample. [...]

By: Greg Allard

Greg Allard — Fri, 31 Oct 2008 17:50:08 +0000

OLD and NEW are used on UPDATE triggers. OLD.col_names will access the data that is in the row of the database before the UPDATE query runs and NEW.col_names will access the data that the row will be updated to.

IF OLD.first_name != NEW.first_name

That checks if the UPDATE query is changing the information for first_name.

By: mysqlearner

mysqlearner — Fri, 31 Oct 2008 14:33:53 +0000

hi ,
please can u explain what is
OLD.first_name != NEW.first_name
are they table names?
I need to write atrigger to get the changed row and also how do i get the same query either insert,update or delete.
thanks in advance