mysql GROUP_CONCAT [英] mysql GROUP_CONCAT

问题描述

我想列出所有具有相应用户类别的用户. 这是我的桌子的简化版本

I want to list all users with their corropsonding user class. Here are simplified versions of my tables

CREATE TABLE users (
    user_id INT NOT NULL AUTO_INCREMENT,
    user_class VARCHAR(100),
    PRIMARY KEY (user_id)
);
INSERT INTO users VALUES
    (1, '1'),
    (2, '2'),
    (3, '1,2');
CREATE TABLE classes (
    class_id INT NOT NULL AUTO_INCREMENT,
    class_name VARCHAR(100),
    PRIMARY KEY (class_id)
);
INSERT INTO classes VALUES
    (1, 'Class 1'),
    (2, 'Class 2');

这是我要使用的查询语句，但仅返回第一个匹配的用户类，而不是希望的连接列表.

And this is the query statement I am trying to use but is only returning the first matching user class and not a concatenated list as hoped.

SELECT user_id, GROUP_CONCAT(DISTINCT class_name SEPARATOR ",") AS class_name
FROM users, classes
WHERE user_class IN (class_id)
GROUP BY user_id;

实际输出

+---------+------------+
| user_id | class_name |
+---------+------------+
|       1 | Class 1    |
|       2 | Class 2    |
|       3 | Class 1    |
+---------+------------+

想要的输出

+---------+---------------------+
| user_id | class_name          |
+---------+---------------------+
|       1 | Class 1             |
|       2 | Class 2             |
|       3 | Class 1, Class 2    |
+---------+---------------------+

预先感谢

推荐答案

这不是最佳设计，但这是您想要的查询:

This is not the best design, but here's the query you want:

SELECT  user_id, GROUP_CONCAT(class_name)
FROM    users
JOIN    classes
ON      FIND_IN_SET(class_id, user_class)
GROUP BY
        user_id

这篇关于mysql GROUP_CONCAT的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！