mysql - 获取未下订单产品的男性用户总数和女性用户总数

Question

如何获得未下订单产品的女性用户总数、男性用户总数以及(男性和女性用户的总和)。结果应如下所示:

total male     | total female     | total
---------------------------------------
 31            |      24          |  55
---------------------------------------

fiddle 帮助http://sqlfiddle.com/#!9/3a0e30/36

之前的代码:

select p.*,
   (select count(*)
    from users u 
    where u.uid not in (select o.uid from       orders o where o.productid = p.productid) and 
          u.gender = 'Male'
   ) as NumMales,
   (select count(*)
    from users u 
    where u.uid not in (select o.uid from orders o where o.productid = p.productid) and 
          u.gender = 'Female'
   ) as NumFemales     

来自产品p；

Answer 1

抱歉，我一开始没理解你的问题，我以为你是在尝试计算用户数量，结果发现你是在尝试计算每个尚未下单的人可能购买的产品订单。

SELECT SUM(CASE WHEN gender = 'Male' THEN 1
           ELSE 0
           END) as Male,
       SUM(CASE WHEN gender = 'Female' THEN 1
           ELSE 0
           END) as Female,
       COUNT(1) as Total
FROM Users U INNER JOIN Products P
LEFT JOIN Orders O ON O.uid = U.uid AND P.productid = O.productid
WHERE O.uid IS NULL

sqlfiddle 此查询返回与之前的查询相同的结果，但不使用 IN 子句，因此可能会更快。

SELECT P.productid,P.productname,P.productdescription,
       SUM(CASE WHEN gender = 'Male' THEN 1
           ELSE 0
           END) as Male,
       SUM(CASE WHEN gender = 'Female' THEN 1
           ELSE 0
           END) as Female,
       COUNT(1) as Total
FROM Users U INNER JOIN Products P
LEFT JOIN Orders O ON O.uid = U.uid AND P.productid = O.productid
WHERE O.uid IS NULL
GROUP BY P.productid,P.productname,P.productdescription