[英]Create mysql unique key based on three columns and a specific value
I have a table with a unique index across two columns user_id
and country_id
我有一个表,该表在两列user_id
和country_id
上具有唯一索引
I have added a new column deleted_at
so I can delete rows whilst keeping the data. 我添加了一个新列deleted_at
以便可以在保留数据的同时删除行。
I would now like to update the unique key so that it is based on user_id
, country_id
and where deleted_at
IS NULL. 我现在想更新唯一键,使其基于user_id
, country_id
以及deleted_at
NULL的位置。 Is this possible, if so how? 如果可能的话,这可能吗?
+----+---------+------------+------------+
+ id | user_id | country_id | deleted_at |
+----+---------+------------+------------+
+ 2 | 3 | 1 | NULL |
+ 3 | 3 | 1 | 2012-10-16 |
| 4 | 3 | 1 | 2012-10-15 |
+----+---------+------------+------------+
Using the above as reference, rows could not be added because of id 2, however if row 2 was not set a new row could be created. 使用以上内容作为参考,由于ID为2,因此无法添加行,但是,如果未设置第2行,则可以创建新行。
Modifying your table mytable should do the trick: 修改表mytable应该可以解决问题:
alter table mytable drop index user_country;
alter table mytable add
unique index user_country_deleted (user_id, country_id, deleted_at);
Edit: I was too quick. 编辑:我太快了。 According to CREATE INDEX Syntax this works only for BDB storage. 根据CREATE INDEX语法,这仅适用于BDB存储。
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