技術標籤：Javasql資料庫mysql

有兩張表A，B，主表詭異的設計， 將使用者表的id用逗號分隔做欄位儲存。
而現在想要看每個使用者的資訊，就得把id逗號拼接做拆分。

模擬了一張order表

模擬了一張order_user表

1. 把逗號拼接的id做拆分做一張臨時表出來

		select a.ID, substring_index(substring_index(a.users, ',', b.help_topic_id + 1), ',', -1) users
	    from `order` a join
						mysql.help_topic b
						on
 
 b.help_topic_id < (length(a.users) - length(replace(a.users, ',', '')) + 1)
		order by a.ID

2. 拆分後的臨時表和使用者表做關聯 獲取使用者資訊

select temp.*, user.user_name, user.email
from (
			 select a.ID, substring_index(substring_index(a.users, ',', b.help_topic_id + 1), ',', -1) users
			 from `order` a
							join
 

						mysql.help_topic b
						on b.help_topic_id < (length(a.users) - length(replace(a.users, ',', '')) + 1)
			 order by a.ID
		 ) temp left join order_user user on temp.users = user.id
order by temp.id

3. 或者用group by ，繼續使用逗號拼接成一個欄位（具體看需求）

select temp.id, group_concat(temp.users), group_concat(
 
user.user_name) user_name, group_concat(user.email) email
from (
			 select a.ID, substring_index(substring_index(a.users, ',', b.help_topic_id + 1), ',', -1) users
			 from `order` a
							join
						mysql.help_topic b
						on b.help_topic_id < (length(a.users) - length(replace(a.users, ',', '')) + 1)
			 order by a.ID
		 ) temp left join order_user user on temp.users = user.id
              group by temp.id
order by temp.id