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
haverun 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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