Question

我有2张桌子：成员，订单。

Members: MemberID, DateCreated
Orders:  OrderID, DateCreated, MemberID

我想知道一个月内新成员的数量，这些成员被分解为多个订单组，例如。 5 +，4,3,2,1,0

我有查询来计算成员的订单数量，但我怎样才能在一个查询中获得这些值？

SELECT
  COUNT(o.orderid) AS Purchases
FROM
  members m
  LEFT JOIN orders o ON o.memberid = m.memberid
    AND MONTH(o.DateCreated) = 8
WHERE
  MONTH(m.DateCreated) = 8
GROUP BY
  m.memberid
ORDER BY
  COUNT(o.orderid) DESC

Answer 1

有几种方法可以做到这一点，其中一些可能相当复杂。

这就是我的方式，专注于新成员而不是计数部分：

  SELECT COUNT(M.MemberID),
         (SELECT COUNT(*) FROM Orders O WHERE O.MemberId = M.MemberId AND O.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)) AS num_orders
    FROM Members M
   WHERE M.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)
GROUP BY num_orders

我使用日期进行查找，因为它会更快（它可以使用索引，而MONTH(M.DateCreated)总是会进行全表扫描，但如果确实需要所有订单/成员，您可以将其更改回来从某个月开始。）

编辑：我忘了处理问题的5+部分，所以这里有一个选项：

  SELECT COUNT(M.MemberID),
         (SELECT IF(COUNT(*) >= 5, '5+', COUNT(*)) FROM Orders O WHERE O.MemberId = M.MemberId AND O.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)) AS num_orders
    FROM Members M
   WHERE M.DateCreated BETWEEN '2010-08-01' AND DATE_ADD('2010-08-01', INTERVAL 1 MONTH)
GROUP BY num_orders

同一查询中的COUNT和子COUNT

2 个答案: