如何基于主表中的值从另一个表中选择另外两个列? [英] How to select two additional columns from another table based on values in the main table?

问题描述

我有一个名为maintable的表，其中有3列:id，userid1和userid2.

I have a table named maintable with 3 columns: id, userid1 and userid2.

另一个名为users的表由userid键控，并以name作为列.

Another table named users is keyed by userid, and has name as a column.

我想选择以下内容:

SELECT maintable.*, users.name AS username1, users.name AS username2 
FROM maintable, users 
WHERE ...

基本上，我想获取maintable行中的所有列，并在末尾添加两列，以从users表中绘制userid1和userid2的名称.

Basically I want to get all the columns in the maintable row, and add two columns at the end that will draw the names for userid1 and userid2 from the users table.

我不确定如何为这样的查询设置where子句的格式.

I'm unsure how to format the where clause for a query like this.

推荐答案

您需要与用户加入两次:

You need to join twice with users:

SELECT m.*, u1.name, u2.name
FROM maintable m 
INNER JOIN users u1 ON (m.userid1 = u1.userid)
INNER JOIN users u2 ON (m.userid2 = u2.userid)

您可以在此处阅读有关MySQL JOIN语法的文档.

You can read the documentation about MySQL JOIN Syntax here.

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