Mysql Split String and Select with results

正規化について考える必要があります。ただし、現在のスキーマについては、次のことを考慮してください

mysql> select * from frontend_users ;
+------+-----------+---------+
| uid  | usergroup | name    |
+------+-----------+---------+
|    1 | 1,2,3     | Michael |
|    2 | 2         | Tobias  |
|    3 | 1         | Colin   |
+------+-----------+---------+
3 rows in set (0.00 sec)

mysql> select * from usergroup ;
+------+----------+
| uid  | title    |
+------+----------+
|    1 | member   |
|    2 | reporter |
|    3 | admin    |
+------+----------+
3 rows in set (0.00 sec)

目的の結果を得るには、次のクエリを使用できますが、これは長期的には効率的ではありません

select 
u.uid,
u.name, 
group_concat(g.title) as groups 
from frontend_users u 
join usergroup g on find_in_set(g.uid,u.usergroup) > 0 
group by u.uid ;

+------+---------+-----------------------+
| uid  | name    | groups                |
+------+---------+-----------------------+
|    1 | Michael | admin,reporter,member |
|    2 | Tobias  | reporter              |
|    3 | Colin   | member                |
+------+---------+-----------------------+

ここで、より良いアプローチは、関連付けテーブルを次のように作成することです

mysql> create table user_to_group (uid int, gid int);
Query OK, 0 rows affected (0.15 sec)

mysql> insert into user_to_group values (1,1),(1,2),(1,3),(2,2),(3,1);
Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0

そして、より良いクエリは

select 
u.uid,
u.name, 
group_concat(g.title) as groups 
from frontend_users u 
join user_to_group ug on ug.uid = u.uid 
join usergroup g on g.uid = ug.gid 
group by u.uid ;

+------+---------+-----------------------+
| uid  | name    | groups                |
+------+---------+-----------------------+
|    1 | Michael | member,admin,reporter |
|    2 | Tobias  | reporter              |
|    3 | Colin   | member                |
+------+---------+-----------------------+