MYSQL連接查詢返回空結果

Question

hobby_users表：

subcategory_master表：

我的查詢：

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') 

實際結果：

預期結果：

注：子查詢retuns 1,2

請建議或幫助我錯了。

Answer 1

對於GROUP_CONCAT你應該使用GROUP BY進行分組

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)