Question

Like, there is top keyword in sql server 2005, how to select top 1 row in mysql if i have join on multiple table & want to retrieve extreme of each ID/column. Limit restricts the no. of row returns so it can’t solve my problem.

Answer 1

SELECT  v.*
FROM    document d
OUTER APPLY
        (
        SELECT  TOP 1 *
        FROM    version v
        WHERE   v.document = d.id
        ORDER BY
                v.revision DESC
        ) v

or

SELECT  v.*
FROM    document d
LEFT JOIN
        (
        SELECT  *, ROW_NUMBER() OVER (PARTITION BY v.id ORDER BY revision DESC)
        FROM    version
        ) v
ON      v.document = d.id
        AND v.rn = 1

The latter is more efficient if your documents usually have few revisions and you need to select all or almost all documents; the former is more efficient if the documents have many revisions or you need to select just a small subset of documents.

Update:

Sorry, didn’t notice the question is about MySQL.

In MySQL, you do it this way:

SELECT  *
FROM    document d
LEFT JOIN
        version v
ON      v.id = 
        (
        SELECT  id
        FROM    version vi
        WHERE   vi.document = d.document
        ORDER BY
                vi.document DESC, vi.revision DESC, vi.id DESC
        LIMIT 1
        )

Create a composite index on version (document, revision, id) for this to work fast.