Re: Complicated "group by" question

Excellent - thanks, Josh!

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Andrew J Perrin - http://www.unc.edu/~aperrin
Assistant Professor of Sociology, U of North Carolina, Chapel Hill
clists@perrin.socsci.unc.edu * andrew_perrin (at) unc.edu


On Wed, 25 Aug 2004, Josh Berkus wrote:

> Andrew,
>
> > I have a table of people ("reviewers"), a table of review assignments
> > ("assign"), and a table of review acceptances ("accept"). I would like to
> > be able to write a query to return the latest (e.g., max(assign_date))
> > assignment for each reviewer, plus the acc_id field from "accept".  I
> > think I should be able to do this with a GROUP BY clause, but am having no
> > luck.
>
> Some vagueness: you didn't say whether you wanted to see two assignments if
> they have the same, latest date.   Nor did you specify whether you wanted to
> see assignments that had not been accepted (the below assumes yes to both)
>
> Hmmm ... one way, SQL-standard:
>
> SELECT reviewer.name, assign_date, acc_id
> FROM reviewers JOIN assign ON reviewer.id = assign.reviewer_id
>     LEFT OUTER JOIN accept ON assign.id = accept.assign_id
> WHERE assign_date IN (SELECT max(ass2.assign_date) FROM assign ass2
>     WHERE ass2.reviewer_id = reviewers.id)
>
> or for a bit faster execution on PG you cann replace that WHERE clause with:
>
> WHERE assign_date IN (SELECT ass2.assign_date FROM assign ass2
>     WHERE ass2.reviewer_id = reviewers.id ORDER BY ass2.assign_date DESC LIMIT 1)
>
> --
> Josh Berkus
> Aglio Database Solutions
> San Francisco
>