Question

I’m having trouble figuring out the SQL statement to retrieve a specific set of data. Where all columns are equal except the last update date, I want the most recent. For example.

Book    Author   Update
John    Foo      1/21/2010
John    Foo      1/22/2010
Fred    Foo2     1/21/2010
Fred    Foo2     1/22/2010

What’s the query that retrieves the most recent rows? That is, the query that returns:

Book    Author   Update
John    Foo      1/22/2010
Fred    Foo2     1/22/2010

TIA,
Steve

Answer 1

SELECT
    book,
    author,
    MAX(update)
FROM
    My_Table
GROUP BY
    book,
    author

This only works in this particular case because all of the other columns have the same value. If you wanted to get the latest row by book, but where the author (or some other column that you will retrieve) might be different then you could use:

SELECT
    T.book,
    T.author,
    T.update
FROM
    (SELECT book, MAX(update) AS max_update FROM My_Table GROUP BY book) SQ
INNER JOIN My_Table T ON
    T.book = SQ.book AND
    T.update = SQ.max_update