Re: [SQL] problem with OR'ed AND queriess

Michael McCarthy wrote:

> Hello David:
>
> Thanks for the quick reply; it means a lot to me.
>
> I tried "SET ksqo TO 'on'", and it works fine for my problem query; it
> allowed 570 key sets to be resolved in 2 seconds, which is a big step
> forward.
>
> I am writing a layer which makes postgres one RDBMS (of several) which can
> support a generic object persistence framework. The use of "SET ksqo TO
> 'on'" is a postgres implementation detail which applications using the
> framework will not be aware of. I am faced with the problem of whether or
> not to use "SET ksqo TO 'on'" for all queries, or find some criteria for
> turning it on and off.
>
> A quick examination of backend/optimizer/prep/prepkeyset.c shows me that
> there is some qualification of a query for keyset optimization; is there
> any reason why I should not always set ksqo on?

The qualification is strict so that it can be left on without breaking other queries.   Most MS ODBC users
use it all the time; I have yet to hear of it causing any problems.

>
>
>
> > There is a work around feature that works for queries that gererate a parse tree similar to yours.
> > ODBC tools generate these kinds of queries all the time.    Keyset queries.   To acivate the
> > feature:    SET ksqo TO 'on';    It rewrites the parse tree into a series of UNIONs.   Not optimal but
> > it works for rectangular where clauses.   (n ANDs) x  (m ORs)
> >
> > --   Here is an example using a 3 part key
> >      select ... from foo where
> >          (v1 = "?" AND v2 = "?" AND v3 ="?") OR        -- line 1
> >          (v1 = "?" AND v2 = "?" AND v3 ="?") OR        -- line 2
> >                  ...
> >          (v1 = "?" AND v2 = "?" AND v3 ="?") OR        --  line 9
> >          (v1 = "?" AND v2 = "?" AND v3 ="?");              --  line 10
> >      --  The question marks are replaced with the constant key values
>
> ************