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Implement GROUP LIMIT and GROUP ORDER BY for easy groupwise maximum

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My idea is to allow anyone to edit the proposal, but to keep a wiki-like history of all edits (initial version would only store the revision info, in later versions we could add an interface for showing them).

Proposed by: Kristian Nielsen, Kristian Nielsen Consulting. 

Idea is to implement a simple syntax for the
classical group-wise maximum problem (http://kristiannielsen.livejournal.com/7357.html).

For a single row, this is easy with ORDER BY FIELD LIMIT 1. But this does not
work for multiple rows with GROUP BY.

Idea is to implement a version of ORDER BY and a version of LIMIT that works
within each group of a GROUP BY query.

Votes: 2    Financial commit: €0

Comment by Kristian Nielsen, Kristian Nielsen Consulting: 

Hm, actually I am not sure I like this proposal the best. It seems maybe
overly complex to allow the GROUP LIMIT. Maybe GROUP ORDER BY would be
sufficient, so that the MySQL extension of allowing non-aggregate fields
outside of the GROUP BY expressions could be made to deterministically select
min/max row. Or maybe a multi-column SELECT EXTREMA(field1 MAX, field2 MIN)
would be better instead.

Comment by Someone: 

Another comment here...

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