加入两个子查询别名答案

【问题标题】：Join two subqueries aliases加入两个子查询别名
【发布时间】：2018-08-10 00:53:39
【问题描述】：

我已经在这里找到了许多类似的请求，但不幸的是，没有什么是相同的。我尝试链接两个子查询，但不知何故它不起作用。这是我的代码：

SELECT a_id, a_sid, a_pid, a_trait1, a_trait2, a_trait3 FROM 
(SELECT 
id AS a_id, sid AS a_sid, pid AS a_pid, max(trait1) AS a_trait1, trait2 AS a_trait2, trait3 AS a_trait3 
FROM 
table_a 
GROUP BY 
sid) AS derived_a, 
(SELECT 
id AS s_id, trait10 AS s_trait10, trait11 AS s_trait11, trait12 AS s_trait12 
FROM 
table_s) AS derived_s 
LEFT JOIN 
derived_a ON derived_a.a_sid = derived_s.s_id

【问题讨论】：

到底是什么问题？你有错误吗？错误的结果？
错误是：SQL 查询中的错误 (1146)：表 'derived_a' 不存在。我想我需要指定我定义的别名。但不知何故，它无论如何都不起作用。

标签： mysql join subquery

【解决方案1】：

错误的sintax，你应该为子查询使用左连接而不是连接别名

  SELECT a_id, a_sid, a_pid, a_trait1, a_trait2, a_trait3 
  FROM  ( 
      SELECT  id AS a_id, sid AS a_sid, pid AS a_pid
        , max(trait1) AS a_trait1, trait2 AS a_trait2, trait3 AS a_trait3 
      FROM  table_a 
      GROUP BY id
  ) AS derived_a 
  left JOIN  (
      SELECT id AS s_id, trait10 AS s_trait10
        , trait11 AS s_trait11, trait12 AS s_trait12 
      FROM table_s) AS derived_s  ON derived_a.a_sid = derived_s.s_id

【讨论】：

谢谢，这是我从未尝试过的方式。但它必须被称为“GROUP BY sid”。如果 id 是唯一的，“GROUP BY id”什么也不做。