Mysql 与联接有关的问题

我有以下查询，其中我使用了

JOIN

s。它说：

未知列m.bv

你能看一下，告诉我我做错了什么吗

$query4 =  'SELECT u.*, SUM(c.ts) AS total_sum1, SUM(m.bv) AS total_sum 
FROM users u 
LEFT JOIN 
 (SELECT user_id ,SUM(points) AS ts FROM coupon GROUP BY user_id) c 
 ON u.user_id=c.user_id 
LEFT JOIN 
 (SELECT user_id ,SUM(points) AS bv FROM matching GROUP BY user_id) r 
ON u.user_id=m.user_id 
where u.user_id="'.$_SESSION['user_name'].'"
GROUP BY u.user_id';

---

如果从别名为

r

的表中选择

SUM（points）AS bv

，则没有别名为

m

的表。因此它必须是

r.bv

，而不是像这样：

SELECT 
  u.*, 
  SUM(c.ts) AS total_sum1, 
  SUM(r.bv) AS total_sum 
FROM users u 
LEFT JOIN 
(
    SELECT 
      user_id,
      SUM(points) AS ts 
    FROM coupon 
    GROUP BY user_id
) c ON u.user_id=c.user_id 
LEFT JOIN 
(
    SELECT 
      user_id,
      SUM(points) AS bv 
     FROM matching 
     GROUP BY user_id
) r ON u.user_id = m.user_id 
where u.user_id="'.$_SESSION['user_name'].'"
GROUP BY u.user_id

---

用r代替m。查看第二个Join

您用

r

为派生表添加了别名，并用

m

引用该表（两次）。纠正其中一个

由于您在两个子查询中按

user\u id

分组，并且

user\u id

是（我假设）表

user

的主键，因此您实际上不需要最后的

按

分组

如果是为所有（许多）用户编写的，我会这样写：

在您（一个用户）的情况下：

最后一个查询也可以简化为：

SELECT u.*, 
     COALESCE( (SELECT SUM(points) FROM coupon 
                WHERE user_id = u.user_id)
             , 0) AS total_sum1,
     COALESCE( (SELECT SUM(points) FROM matching 
                WHERE user_id = u.user_id)
             , 0) AS total_sum 
FROM users u 
WHERE u.user_id = "'.$_SESSION['user_name'].'"

查询中没有表“m”。请不要使用大写字母

SELECT u.*, COALESCE(c.ts, 0) AS total_sum1, COALESCE(m.bv, 0) AS total_sum 
FROM users u 
  LEFT JOIN 
     (SELECT SUM(points) AS ts FROM coupon
      WHERE user_id = "'.$_SESSION['user_name'].'") c 
    ON TRUE 
  LEFT JOIN 
     (SELECT SUM(points) AS bv FROM matching
      WHERE user_id = "'.$_SESSION['user_name'].'") m
   ON TRUE 
WHERE u.user_id = "'.$_SESSION['user_name'].'"

SELECT u.*, 
     COALESCE( (SELECT SUM(points) FROM coupon 
                WHERE user_id = u.user_id)
             , 0) AS total_sum1,
     COALESCE( (SELECT SUM(points) FROM matching 
                WHERE user_id = u.user_id)
             , 0) AS total_sum 
FROM users u 
WHERE u.user_id = "'.$_SESSION['user_name'].'"