Trying to get the average of a count resultset

Question

I have the following SQL:(bitemp)

SELECT COUNT (*) AS Count
  FROM Table T
 WHERE (T.Update_time =
           (SELECT MAX (B.Update_time )
              FROM Table B
             WHERE (B.Id = T.Id))
GROUP BY T.Grouping

now I am getting a resultset with a lot of numbers. I want to get the average of this list. At the moment, I am importing the list into excel and use its average function. But there is a AVG function for DB2, but I did not get it to work.

I tried SELECT AVG(COUNT(*)) and also SELECT AVG(*) FROM (theQuery).

Answer 1

You just can put your query as a subquery:

SELECT avg(count)
  FROM 
    (
    SELECT COUNT (*) AS Count
      FROM Table T
     WHERE T.Update_time =
               (SELECT MAX (B.Update_time )
                  FROM Table B
                 WHERE (B.Id = T.Id))
    GROUP BY T.Grouping
    ) as counts

Edit: I think this should be the same:

SELECT count(*) / count(distinct T.Grouping)
  FROM Table T
 WHERE T.Update_time =
           (SELECT MAX (B.Update_time)
              FROM Table B
             WHERE (B.Id = T.Id))