Re: [BUGS] Bug in 6.4.2. Aggregate/View/Where-condition

On Mon, 28 Feb 2000, Tom Lane wrote:


> regression=# select * from span where min > 3;
>  ref | min | max
> -----+-----+-----
> (0 rows)

Note that under 6.4 and 6.5, the result of a aggregate (or a subquery,
even) has to be on the RHS Of an operator. Viz:

test1=> select * from span where min>0;
ERROR:  rewrite: aggregate column of view must be at rigth side in

The fact that this error does not come up in 7 either means that they've
fixed a limitation, or there's a bug that's crept in. Can you try it with

select * from span where 3<min;

and see what you get.


> Ooops.  (I think the problem here is that the WHERE clause really needs
> to be a HAVING clause after the rule is expanded, since that "min" is
> really an aggregate invocation --- but the rewriter isn't smart enough
> to make that change.)

Okay... here's a test under 6.5.2:

test1=> select * from span having 0<min;
ERROR:  SELECT/HAVING requires aggregates to be valid

Oops.

Does this work under 7.beta?


>
> The bottom line is that grouped views don't work right in any but the
> very simplest cases, and they can't work right given the current
> implementation of rules.  We need to redesign the internal querytree
> data structure to support explicit subqueries.  I hope to see that
> happen for 7.1, but it's not done or even started as of today.
>
> Sorry the news isn't better :-(

Thanks tons for trying that out for me, tom. Hope that gives our kind,
wonderful developers food for thought :)


(PS... just in case having min and max as column names in the view was
giving 6.4 or 6.5 headaches, I've repeated /all/ the tests using different
names for the columns, with no apparent change in results)



   ("`-/")_.-'"``-._        Ch'marr, a.k.a.
    . . `; -._    )-;-,_`)  Chris Cogdon <chris@felidae.apana.org.au>
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