Mysql SQL使用子句汇总数据

例如，我有两个表：

使用者

付款

+---------+--------+------+
| user_id | amount | case |
+---------+--------+------+
|     0   |   10   |   1  |
|     0   |    1   |   2  |
|     2   |    5   |   1  |
|     2   |    4   |   1  |
|     2   |    5   |   2  |
|     3   |   26   |   2  |
+---------+--------+------+

我试图得到输出：

+---------+---------------------+---------------------+
| user_id | total_amount_case_1 | total_amount_case_2 |
+---------+---------------------+---------------------+
|     0   |                10   |                  1  |
|     2   |                 9   |                  5  |
|     3   |                 0   |                 26  |
+---------+---------------------+---------------------+

用文字解释我试图选择每个至少有一笔付款的用户，并在不同的情况下对其付款金额进行合计

我可以选择每个用户的总付款，但不取决于具体情况：

SELECT users.id AS user_id, SUM(payments.amount) AS total_amount FROM users LEFT JOIN users.id = payments.user_id GROUP BY user_id ORDER BY user_id;

这给了我这个输出：

+---------+--------------+
| user_id | total_amount |
+---------+--------------+
|     0   |         11   |
|     1   |          0   |
|     2   |         14   |
|     3   |         26   |
+---------+--------------+

---

您可以通过条件聚合实现这一点——在聚合函数中使用

case

语句：

SELECT u.id AS user_id,
       SUM(case when p.`case` = 1 then p.amount else 0 end) AS total_amount_case1,
       SUM(case when p.`case` = 2 then p.amount else 0 end) AS total_amount_case2
FROM users u LEFT JOIN 
     payments p
     on u.id = p.user_id
GROUP BY user_id
ORDER BY user_id;

我还添加了表别名，以减少查询的麻烦。

试试这个

SELECT 
  u.id AS user_id,
  SUM(CASE WHEN p.`case` = 1 THEN p.amount ELSE 0 END) AS total_amount_case_1,
  SUM(CASE WHEN p.`case` = 2 THEN p.amount ELSE 0 END) AS total_amount_case_2 
FROM
  users u
  LEFT JOIN payments p ON u.id = p.user_id 
GROUP BY u.user_id 
ORDER BY u.user_id ;

---

我会做以下几点：

SELECT users.id
,SUM(CASE WHEN payments.[case] = 1 THEN total_amount_case_1 ELSE 0 END) as total_amount_case_1
,SUM(CASE WHEN payments.[case] = 2 THEN total_amount_case_2 ELSE 0 END) as total_amount_case_2
FROM users INNER JOIN payments
ON users.id = payments.user_id
GROUP BY payments.user_id

SELECT users.id AS user_id, 
   SUM(case when Payments.Case = 1 then payments.amount else 0 End) AS total_amount_case1, 
   SUM(case when Payments.Case = 2 then payments.amount else 0 End) AS total_amount_case2  
FROM users LEFT JOIN payments on
   users.id = payments.user_id 
GROUP BY users.id
ORDER BY users.id;

SELECT users.id As user_id
     , Sum(CASE WHEN payments.case = 1 THEN payments.amount ELSE 0 END) As total_amount_case_1
     , Sum(CASE WHEN payments.case = 2 THEN payments.amount ELSE 0 END) As total_amount_case_2
FROM   users
 LEFT
  JOIN payments
    ON users.id = payments.user_id
GROUP
    BY user_id
ORDER
    BY user_id;

SELECT users.id
,SUM(CASE WHEN payments.[case] = 1 THEN total_amount_case_1 ELSE 0 END) as total_amount_case_1
,SUM(CASE WHEN payments.[case] = 2 THEN total_amount_case_2 ELSE 0 END) as total_amount_case_2
FROM users INNER JOIN payments
ON users.id = payments.user_id
GROUP BY payments.user_id