问题描述
id home path name layer
1 /home test user1 1
2 /etc test2 user2 1
3 /home test user3 1
4 /home test user4 1
5 /home test user1 1
6 /etc test2 user2 1
如果 home
、path
和 name
相等,但仅当所有 3 个都相同时,我如何删除所有重复项?
sl id 1 应该被删除,因为它是 id 5 的副本,而 id 2 应该删除,因为它是 id 6 的副本。
它应该是这样的:
id home path name layer
3 /home test user3 1
4 /home test user4 1
5 /home test user1 1
6 /etc test2 user2 1
解决方法
您可以通过 group by
实现这一目标:
select
*
from data
group by "home","path","name"
having max("id")
order by "id"
,
如果您确实想删除重复项,请使用存在逻辑:
DELETE
FROM yourTable
WHERE EXISTS (SELECT 1 FROM yourTable t2
WHERE t2.home = yourTable.home AND
t2.path = yourTable.path AND
t2.name = yourTable.name AND
t2.id > yourTable.id);
如果您只想以这种方式查看您的数据,请尝试:
SELECT t1.*
FROM yourTable t1
WHERE NOT EXISTS (SELECT 1 FROM yourTable t2
WHERE t2.home = t1.home AND t2.path = t1.path AND
t2.name = t1.name AND t2.id > t1.id);
,
您可以按列 home
、path
、name
进行分组,然后选择 MAX(id)
。
在这种情况下,SQLite 将为 3 列的每个组合仅返回 1 行,即最大 id
行:
SELECT MAX(id) id,home,path,name,layer
FROM tablename
GROUP BY home,name
ORDER BY id
这是documented feature of SQLite。
如果要删除重复项:
DELETE FROM tablename
WHERE id NOT IN (SELECT MAX(id) FROM tablename GROUP BY home,name)
参见demo。
结果:
id | home | 路径 | 名称 | 层 |
---|---|---|---|---|
3 | /home | 测试 | user3 | 1 |
4 | /home | 测试 | user4 | 1 |
5 | /home | 测试 | user1 | 1 |
6 | /etc | test2 | user2 | 1 |