MYSQL-JOIN查询返回空结果

Question

hobby_users表：

subcategory_master表：

我的查询：

SELECT hobby_users.user_subcategory_id,GROUP_CONCAT(subcategory_master.subcategory_name) AS subcategory_name
        FROM `hobby_users` 
        INNER JOIN subcategory_master
        WHERE hobby_users.hobby_users_id='1' AND subcategory_master.subcategory_master_id IN(SELECT user_subcategory_id FROM `hobby_users` WHERE hobby_users_id='1')

实际结果：

预期结果：

注意：子查询返回1,2

请建议或帮助我错了。

Answer 1

对于group_concat，您应该使用GROUP BY进行分组

SELECT 
   hobby_users.user_subcategory_id
  ,GROUP_CONCAT(subcategory_master.subcategory_name) AS subcategory_name
FROM `hobby_users` 
INNER JOIN subcategory_master
WHERE hobby_users.hobby_users_id='1' 
  AND subcategory_master.subcategory_master_id IN (SELECT user_subcategory_id FROM `hobby_users` WHERE hobby_users_id='1')
GROUP BY hobby_users.user_subcategory_id

Answer 2

/*
drop table if exists hobby_users;
create table hobby_users(hobby_users_id int, user_name varchar(3), user_subcategory_id varchar(3));

drop table if exists subcategory_master;
create table subcategory_master(subcategory_master_id int, subcategory_name varchar(3));

insert into hobby_users values
(1,'abc','1,2'),
(2,'def','1,3');

insert into subcategory_master values
(1,'aaa'),(2,'bbb'),(3,'ccc'),(4,'ddd');
*/


MariaDB [sandbox]> SELECT h.hobby_users_id,
    ->    h.user_subcategory_id
    ->   ,GROUP_CONCAT(sm.subcategory_name) AS subcategory_name
    -> FROM `hobby_users` h
    -> INNER JOIN subcategory_master sm
    -> WHERE h.hobby_users_id='1'
    ->   AND
    ->   find_in_set(sm.subcategory_master_id,h.user_subcategory_id) > 0
    -> GROUP BY h.user_subcategory_id;
+----------------+---------------------+------------------+
| hobby_users_id | user_subcategory_id | subcategory_name |
+----------------+---------------------+------------------+
|              1 | 1,2                 | aaa,bbb          |
+----------------+---------------------+------------------+
1 row in set (0.00 sec)