Re: [SQL] index usage ... strange !?

> Marten Feldtmann <marten@feki.toppoint.de> writes:
> >  SELECT AO,AT,AV FROM P3AT
> >  WHERE EXISTS( SELECT AO FROM P3AT WHERE AV='12' AND AT=12 AND CI=17)
> 
> Um ... I dunno what you are trying to accomplish, but this query
> almost certainly doesn't do what you want.  Since the inner query
> is independent of the outer, you will get back either all the rows
> of P3AT (if the inner query yields rows) or none (if it doesn't).
> 
> The plan you quote is perfectly reasonable for this query...
> the machine is even bright enough to figure out that it only
> needs to evaluate the subquery once.
> 
>             regards, tom lane
> Yes, this seems to be a wrong statement. Actually  I would write it like:
select AO,AT,AV FROM P3AT WHERE AO IN (SELECT AO FROM P3AT WHERE ...)
but as PostgreSQL does not like "IN" very much I rewrote it to the wrongstatement above.
select P3AT.AO,P3AT.AT,P3AT.AV FROM P3AT,P3AT as B WHERE  (B.AO=P3AT.AO) AND (B.AV='12') AND (B.AT=12) AND (B.CI=17)


Therefore I have to rewrite the sql statement above to:
SELECT P3AT.AV,P3AT.AT,P3AT.AV FROM P3AT  WHEREEXISTS( SELECT B.AO FROM P3AT as B WHERE B.AO=P3AT.AO AND ..... )
Right ?

Marten Feldtmann