Re: Functional dependency in GROUP BY through JOINs

> From: Kevin Grittner [mailto:kgrittn(at)mail(dot)com]
> > I think I'm right in thinking that if a unique index exists to match
> > the group by clause, and the join condition is equality (probably
> > using the same operator class as the unique btree index?), then the
> > grouping could be pushed up to before the join.
>
> Off-hand, it seems equivalent to me; I don't know how much work it would
> be.
>
> Out of curiosity, does the first query's plan change if you run this instead?:
>
> SELECT s.product_code,SUM(s.quantity)
> FROM products p
> INNER JOIN bigsalestable s ON p.productid = s.productid GROUP BY
> s.product_code;
>

I should have made it more clear about the lack of product_code in the bigsalestable, there's only productid, the lookup to the product table was to obtain the actual more user friendly product_code.

The actual table def's are in the attachment of the original email.

Regards

David Rowley

> -Kevin