INNER JOIN 同一个表 [英] INNER JOIN same table

问题描述

我正在尝试从同一个表中获取一些行.这是一个用户表:用户有 user_id 和 user_parent_id.

I am trying to get some rows from the same table. It's a user table: user has user_id and user_parent_id.

我需要获取 user_id 行和 user_parent_id 行.我已经编写了这样的代码:

I need to get the user_id row and user_parent_id row. I have coded something like this:

SELECT user.user_fname, user.user_lname
FROM users as user
INNER JOIN users AS parent
ON parent.user_parent_id = user.user_id
WHERE user.user_id = $_GET[id]

但它没有显示结果.我想显示用户记录及其父记录.

But it doesn't show the results. I want to display user record and its parent record.

推荐答案

我认为问题出在您的 JOIN 条件上.

I think the problem is in your JOIN condition.

SELECT user.user_fname,
       user.user_lname,
       parent.user_fname,
       parent.user_lname
FROM users AS user
JOIN users AS parent 
  ON parent.user_id = user.user_parent_id
WHERE user.user_id = $_GET[id]

编辑:如果用户没有父母，您可能应该使用 LEFT JOIN.

Edit: You should probably use LEFT JOIN if there are users with no parents.

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