Re: fetch updated columns in 'before update' trigger

[Jon Beyer]

> > 'delete and recreate updated trigger'
>
> Can't be done while the Trigger is being invoked.


I think I'm still not getting across what I'm trying to do. I'm not trying to update a trigger while it is being invoked. As it currently stands, if I don't have access to a function inside the trigger that tells me what column is being updated, then I need a clause inside the trigger for every single column. Thus, if a month from now, I add a now column, I need to modify my trigger. This is brittle. So I'm looking for something equivalent to COLUMNS_UPDATED( ) in SQL Server.



>
> > I don't want to have to modify my trigger every
> time I add a column
>
> SQL isn't a complete computer language, Triggers
> and much else need specific table & column specs.
> And, in a correctly designed database, DDL changes
> should be rare except when the requirement changes
> enough to require a major upgrade, so if you
> expect to be adding columns often, what problem
> drives that expectation?

The changes will not be frequent, but it's pretty ugly to have a clause inside a trigger for every single column in the table.


>
> > list of updated columns
>
> You'd need to code that yourself, eg by storing a
> copy of the Update statement in a table and having
> the Trigger retrieve and parse it. But it might
> not be helpful---MySQL doesn't support dynamic SQL
> in Triggers.


This is probably not a good option. I'm using an ORM (ActiveRecord / Rails), so adding the complexity of storing an update statement before executing said statement, reading and parsing said statement from a table, isn't really cleaner than current solution of having a monstrously long trigger.