Re: UPDATE keyword

On Fri, May 25, 2001 at 04:16:00PM -0700, Ian Harding wrote:
> Well, I am making progress in rewriting my MSSQL Server T-SQL triggers and stored procedures in Pl/Tcl.  However, I have run into a bit of an issue and I wonder if anyone knows the best way to address it...
> 
> In T-SQL triggers, you can use the UPDATE keyword in conditional expressions as in 
> 
> IF UPDATE(myfield)
> BEGIN
>     do something
> END
> 
> It detects the update of the field.  I have been comparing
> $NEW(myfield) and $OLD(myfield) which works ok, except where I
> used the UPDATE() test as a crutch.  I sometimes do an update
> like
> 
> UPDATE mytable SET myfield = myfield WHERE...
> 
> to fire an update trigger, and executing only the code in that trigger surrounded by UPDATE(myfield).
> 
> Is there an easy way to duplicate this, or should I work around it?

how about

	create view
		relationname
		as select * from _real_relation_name_;

	create rule
		on update to relationname
		do instead (
			update _real_relation_name_
				set fld=new.fld,
				col=new.col,
				modified=current_timestamp,
				differencefield=old.something-new.something,
				whatever=some_function()
			;
			insert into _some_tracking_relation_
				( field, list, here )
				values
				( ... )
		);

check out the manuals for 'create rule'. very handy stuff.

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