我的表中有重复的行。
我有两个通过外键连接的表
regions (id)
orders (region_id)
这些地区有重复的名称。我想删除这些重复的行并更新订单表,重复的外键现在将设置为仅保留区域表中的现有名称。
Example:
regions table:
id name
1 | test
2 | test
3 | foo
orders table:
id region_id
6 | 1
7 | 2
9 | 3
I want
orders table:
id region_id
6 | 1
7 | 1
9 | 3
regions table:
id name
1 | test
3 | foo
我可以使用以下 SQL 获取重复行:
SELECT name, count(id) as cnt FROM regions
GROUP BY name HAVING cnt > 1
如何将此选择与订单表连接并删除重复的行并更新表?
要更新订单表,类似于:
update orders
join regions r1
on r1.id = orders.region_id
set orders.region_id =
(
select min(r2.id)
from regions r2
where r2.name = r1.name
)
之后,您可以使用以下命令删除重复的行:
delete regions
from regions
where id not in
(
select id
from (
select min(id) as id
from regions
group by
name
) as SubqueryAlias
)
需要双重子查询以避免MySQL错误ERROR 1093 (HY000) at line 36: You can't specify target table 'regions' for update in FROM clause
.
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