Re: Better way to write aggregates?

["Jim Buttafuoco" <jim(at)contactbda(dot)com>]

I don't think an index will help you with this query. 

---------- Original Message -----------
From: Jan Dittmer <jdi(at)l4x(dot)org>
To: jim(at)contactbda(dot)com
Cc: pgsql-performance(at)postgresql(dot)org
Sent: Fri, 21 Apr 2006 14:35:33 +0200
Subject: Re: [PERFORM] Better way to write aggregates?

> Jim Buttafuoco wrote:
> > Jan,
> > 
> > I write queries like this
> > 
> > CREATE VIEW parent_childs AS
> > SELECT
> >  	c.parent,
> >  	count(c.state) as childtotal,
> >  	sum(case when c.state = 1 then 1 else 0 end) as childstate1,
> >  	sum(case when c.state = 2 then 1 else 0 end) as childstate2,
> >  	sum(case when c.state = 3 then 1 else 0 end) as childstate3
> >  FROM child c
> >  GROUP BY parent;
> 
> It would help if booleans could be casted to integer 1/0 :-) But
> performance wise it should be about the same? I think I'll
> run some tests later today with real data.
> Would an index on NULLIF(state,1) help count(NULLIF(state,1)) ?
> Can one build an index on (case when c.state = 3 then 1 else 0 end)?
> 
> Thanks,
> 
> Jan
------- End of Original Message -------