mysql - 同时获取2个相同的字段

Question

我在下面有 3 张桌子。（示例）（mySql 脚本）

顾客

• cust_id
• 客户名称
• 用户身份
• user_id_2

用户

• 用户身份
• em_id

员工

• em_id
• em_name

如何通过与连接同时交叉表调用em_name字段user_id和em_name字段？user_id_2user

Answer 1

尝试这个

SELECT  q1.* ,
        q2.em_name AS 'em_name_2'
FROM    (SELECT c.cust_id ,
                c.cust_name ,
                c.user_id ,
                c.user_id_2 ,
                e.em_name
         FROM   dbo.customer AS c
                INNER JOIN dbo.[user] AS u ON c.user_id = u.user_id
                INNER JOIN dbo.employee AS e ON u.em_id = e.em_id
        ) q1
       CROSS JOIN 
       ( SELECT   e.em_id ,
                  e.em_name
         FROM     dbo.customer AS c
                INNER JOIN dbo.[user] AS u ON c.user_id_2 = u.user_id
                INNER JOIN dbo.employee AS e ON u.em_id = e.em_id
    ) q2