> 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

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