Chris,
> SELECT * FROM (arbitrary subquery) AS sub ORDER BY 1,3;
>
> Now, this all works fine, but I want to know if this is efficient or not.
>
> Does doing a select of a select cause serious performance degradation?
It would be better if you could strip out the inner sort, but I can understand
why that might not be possible in all cases.
The only thing you're adding to the query is a second SORT step, so it
shouldn't require any more time/memory than the query's first SORT did.
--
Josh Berkus
Aglio Database Solutions
San Francisco
