Question

I have a database table which stores membership renewals each year. When insert the renewal record, an ‘expiryDate’ column is written with a date (31/8/[nextyear]).

So, as an example, let’s say a member with memberID = 99 renews in 2007, 2008 and 2009, he will have 3 records (one for each year), with an ‘expiryDate’ recorded in each. If I do a

SELECT MAX(YEAR(expiryDate)) as maxExpiry 
  FROM renewals 
 WHERE memberID = 99

…I will get 2010 back.

What I would like to do is return ALL records where the MAX(YEAR(expiryDate)) is a given year.. for example,

SELECT * 
  FROM renewals 
 WHERE MAX(YEAR(expiryDate)) = '2010';

This query won’t work as an aggregation can’t be used in a where clause outside a subquery, but I can’t quite work out how to structure the subquery… or even if this could be done a better way than using a subquery.

Answer 1

A predicate based on an aggregated column uses a HAVING clause, rather than a WHERE.

If you only need the memberID, this is straightforward enough:

SELECT memberID
  FROM renewals
  GROUP BY memberID
    HAVING MAX(YEAR(expiryDate)) = 2010

You can also do this as a sub-query if you need to get other columns from that table, ie:

SELECT * FROM members
  WHERE memberID IN ( <<previous query>> )

UPDATE

It is correct as @OMG Ponies pointed out that this is not enough if you need to select additional columns from that one row in renewals. If that is required, you could use:

SELECT * FROM renewals
  WHERE memberID IN ( SELECT memberID FROM renewals
                      GROUP BY memberID HAVING MAX(YEAR(expiryDate)) = 2010 )
    AND YEAR(expiryDate) == 2010