加入两个表mysql查询返回所有用户列表值？

Question

加入两个表MySQL查询返回所有用户列表值。 请更正此查询或提供一些查询。

表1：用户

+---------+------------+-----------+
| user_id | user_name  | cource_id |
+---------+------------+-----------+
|       1 | ramalingam | 1,2,3,4   |
|       2 | yuvi       | 1         |
|       3 | Saravanan  | 1,2,3     |
|       4 | gandhi     | 1         |
+---------+------------+-----------+

表2：课程

+-----------+-------------+
| cource_id | cource_name |
+-----------+-------------+
|         1 | php         |
|         2 | wordpress   |
|         3 | seo         |
|         4 | magento     |
+-----------+-------------+

输出

--------------------------------------
user_id | user_name | cource_id
--------------------------------------
1       | ramalingam| php,wordpress,seo,magnto
2       | yuvi      | php
3       | Saravanan | php,wordpress,seo
4       | gandhi    | php

这是我的查询

SELECT u.user_id,u.user_name, GROUP_CONCAT(c.cource_name)as course_name
FROM users as u 
LEFT JOIN course as c ON c.cource_id = u.user_id

感谢您对我的帮助...

Answer 1

一般来说，DB设计很糟糕，根本不要使用逗号分隔列表。您应该在JOIN子句中使用FIND_IN_SET()来实现此目的：

SELECT
    u.user_id,
    u.user_name,
    GROUP_CONCAT(c.cource_name) AS course_name
FROM
    users AS u
LEFT JOIN cource AS c ON FIND_IN_SET(c.cource_id, u.cource_id)
GROUP BY
    u.user_id,
    u.user_name

输出是：

+---------+------------+---------------------------+
| user_id | user_name  | course_name               |
+---------+------------+---------------------------+
|       1 | ramalingam | php,wordpress,seo,magento |
|       2 | yuvi       | php                       |
|       3 | Saravanan  | php,wordpress,seo         |
|       4 | gandhi     | php                       |
+---------+------------+---------------------------+
4 rows in set