我需要从一个相当大的SQL Server表(即300,000+行)中删除重复的行。
当然,由于RowID标识字段的存在,这些行不会完全重复。
MyTable
RowID int not null identity(1,1) primary key,
Col1 varchar(20) not null,
Col2 varchar(2048) not null,
Col3 tinyint not null
我该怎么做呢?
我需要从一个相当大的SQL Server表(即300,000+行)中删除重复的行。
当然,由于RowID标识字段的存在,这些行不会完全重复。
MyTable
RowID int not null identity(1,1) primary key,
Col1 varchar(20) not null,
Col2 varchar(2048) not null,
Col3 tinyint not null
我该怎么做呢?
当前回答
DELETE
FROM MyTable
WHERE NOT EXISTS (
SELECT min(RowID)
FROM Mytable
WHERE (SELECT RowID
FROM Mytable
GROUP BY Col1, Col2, Col3
))
);
其他回答
使用CTE。这个想法是连接一个或多个列,形成一个重复的记录,然后删除你喜欢的:
;with cte as (
select
min(PrimaryKey) as PrimaryKey
UniqueColumn1,
UniqueColumn2
from dbo.DuplicatesTable
group by
UniqueColumn1, UniqueColumn1
having count(*) > 1
)
delete d
from dbo.DuplicatesTable d
inner join cte on
d.PrimaryKey > cte.PrimaryKey and
d.UniqueColumn1 = cte.UniqueColumn1 and
d.UniqueColumn2 = cte.UniqueColumn2;
我更喜欢子查询\having count(*) > 1解决方案内部连接,因为我发现它更容易阅读,它很容易变成一个SELECT语句来验证什么将被删除,然后再运行它。
--DELETE FROM table1
--WHERE id IN (
SELECT MIN(id) FROM table1
GROUP BY col1, col2, col3
-- could add a WHERE clause here to further filter
HAVING count(*) > 1
--)
创建具有相同结构的新空白表 像这样执行查询 插入tc_category1 SELECT * 从tc_category GROUP BY category_id, application_id count(*) > 然后执行这个查询 插入tc_category1 SELECT * 从tc_category GROUP BY category_id, application_id count(*) = 1
我想这会很有帮助。这里,ROW_NUMBER() OVER(分区由res1。Title ORDER BY res1.Id)作为num来区分重复的行。
delete FROM
(SELECT res1.*,ROW_NUMBER() OVER(PARTITION BY res1.Title ORDER BY res1.Id)as num
FROM
(select * from [dbo].[tbl_countries])as res1
)as res2
WHERE res2.num > 1
我想提一下这种方法,它可能是有帮助的,并且适用于所有SQL服务器: 通常只有一到两个副本,副本的id和数量是已知的。在这种情况下:
SET ROWCOUNT 1 -- or set to number of rows to be deleted
delete from myTable where RowId = DuplicatedID
SET ROWCOUNT 0