Question

我知道我在问一些看起来微不足道的东西，但我无法找到并回答或重复。（我是这个领域的新手）。所以我在努力。

我有两张桌子使用以下列测试表

1. storyID , authorID , assigneeID
2. userID , userName

我想写一个返回storyID, UserName of author ID, UserName of assigneeID。

的查询

Answer 1

SELECT storyID, u1.userName AS authorName, u2.userName AS assigneeName 
FROM storytable s 
INNER JOIN usertable u1 ON s.authorID = u1.userID 
INNER JOIN usertable u2 ON s.assigneeID = u2.userID

只有在userID，assigneeID和authorID字段之间存在关联时，上述解决方案才有效。

Answer 2

选择并为第二个表创建别名。

SELECT a.storyID, b.userName, c.userName
FROM tablea a
INNER JOIN tableb b ON a.authorID = b.userID
INNER JOIN tableb c ON a.assigneeID= c.userID

Answer 3

假设authorID = UserId ...

select 
     1.storyId, 
     author.userName,
     assignee.userName 
 from 1
 inner join 2 as author 
      on 1.authorId = 2.userId 
 inner join 2 as assignee
      on 1.assigneeID = 2.userID

在同一个表上编写包含两个约束的查询

3 个答案: