sql - 试图获得计数结果集的平均值

Question

我有以下 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

现在我得到了一个包含很多数字的结果集。我想得到这个列表的平均值。目前，我正在将列表导入 excel 并使用其平均功能。但是 DB2 有一个 AVG 函数，但我没有让它工作。

我试过 SELECT AVG(COUNT(*))还有 SELECT AVG(*) FROM (theQuery) .

Answer 1

您只需将查询作为子查询:

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

编辑:我认为这应该是一样的:

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))