SQLFiddle

Question

在这里，我想加入表格responsibilities＆＃39;使用字段Name, Direct, Supervise：

Name | Direct | Supervise
 ABC    2        4

和表＆＃39;职位＆＃39;使用positionCode，positionID：

positionCode | positionID
   HR/HRM         2
   HR/MN          4

选择的结果表将是这样的。

Name | Direct | Supervise
 ABC   HR/HRM    HR/MN

＆＃39; Direct＆＃39;和＆＃39; Supervise＆＃39;列应该是positionCode来自＆＃39;位置＆＃39;表。是否有一体化查询输出此结果？或者我要查询2次？

Answer 1

尝试此查询，

SELECT r.Name,
       p1.positionCode AS Direct,
       p2.positionCode AS Supervise
FROM responsibilities r
LEFT JOIN positions p1
    ON r.Direct = p1.positionID
LEFT JOIN positions p2
    ON r.Supervise = p2.positionID

输出：SEE SQLFiddle DEMO

Answer 2

我认为您可以responsibilities两次加入positions表：

SELECT r.Name,
       COALESCE(p1.positionCode, 'Direct is N/A') AS Direct,
       COALESCE(p2.positionCode, 'Supervise is N/A') AS Supervise
FROM responsibilities r
LEFT JOIN positions p1
    ON r.Direct = p1.positionID
LEFT JOIN positions p2
    ON r.Supervise = p2.positionID

请按照以下链接查看正在运行的演示：

SQLFiddle

Answer 3

尝试以下查询，它应该可以正常工作

select R.Name,(select P.positionCode where R.Direct=P.positionID) as 
Direct,(select P.positionCode where R.Supervise=P.positionID) as 
Supervise from Responsibilites R, Positions P;

Answer 4

查看此SQL小提琴，了解此查询是否有效：

http://sqlfiddle.com/#!9/13845c/4/0

基本上，查询如下所示：

SELECT r.Name, p1.positionCode As Direct, p2.positionCode as Supervise
FROM responsibilities r 
LEFT JOIN positions p1 ON r.Direct = p1.positionID
LEFT JOIN positions p2 ON r.Supervise = p2.positionID

更改MYSQL中选定结果表中的列

4 个答案:

SQLFiddle