Is there a [straightforward] way to order results *first*, *then* group by another column, with SQL?

Question

I see that in SQL, the GROUP BY has to precede ORDER BY expression. Does this imply that ordering is done after grouping discards identical rows/columns?

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Answer 1

Yes, grouping is done first, and it affects a single select whereas ordering affects all the results from all select statements in a union, such as:

select a, 'max', max(b) from tbl group by a
union all select a, 'min', min(b) from tbl group by a
order by 1, 2

(using field numbers in order by since I couldn't be bothered to name my columns). Each group by affects only its select, the order by affects the combined result set.

It seems that what you're after can be achieved with:

select A, max(B) from tbl group by A

This uses the max aggregation function to basically do your pre-group ordering (it doesn't actually sort it in any decent DBMS, rather it will simply choose the maximum from an suitable index if available).