Re: Trigger on select?

Kyle Bateman wrote:

> Hey, anyone know if it is possible to fire a trigger before a select?
> I'm considering creating some tables which contain data summarized
> from other tables as kind of a cache mechanism. The hope is I can
> speed up some queries that get executed a lot (and are kind of slow)
> by maintaining data (like sums of big columns, for example). I was
> all ready to go and then I discovered that trigger-before-select is
> not supported. (Is it in any DB?)
>
> The idea is this:
>
> Any time I execute a query that would access the summary data, the
> "before select" trigger fires and goes out and builds any summary data
> missing from the summary table.

No. You must instead generate a view.

> When I do an insert,update,delete on the primary data table, another
> trigger fires that removes the applicable data from the summary
> table. This way, I only cache the information I need in the summary
> table, right before I need it. But it can stay there as long as the
> base information doesn't change so I don't have to redo the expensive
> operation of summarizing it any more often than necessary. Its kind
> of like an index in a way, but it is not maintained at insert/update
> time. Rather, it is updated as it is needed.
>
> Anyone have any ideas about how I can accomplish this?

something like create view wrapper_table as
select * from original table where (select pseudo_trigger_function())
IS TRUE;

The above example is off the top of my head. It may require some editing.

Best Wishes,
Chris Travers
Metatron Technology Consulting