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

删除重复记录

在这种情况下,大于操作符删除除第一条记录以外的所有记录

u1 FROM users u1 JOIN users u2 u1的地方。Id > u2.id 和u1.email = u2.email

<小于操作符在这种情况下删除除最后一条记录以外的所有记录

u1 FROM users u1 JOIN users u2 u1的地方。Id < u2.id 和u1.email = u2.email

其他回答

通过使用下面的查询,我们可以基于单列或多列删除重复的记录。下面的查询是基于两列进行删除。表名为:testing,列名为empno,empname

DELETE FROM testing WHERE empno not IN (SELECT empno FROM (SELECT empno, ROW_NUMBER() OVER (PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)
or empname not in
(select empname from (select empname,row_number() over(PARTITION BY empno ORDER BY empno) 
AS [ItemNumber] FROM testing) a WHERE ItemNumber > 1)

对于表结构

MyTable

RowID int not null identity(1,1) primary key,
Col1 varchar(20) not null,
Col2 varchar(2048) not null,
Col3 tinyint not null

删除重复项的查询:

DELETE t1
FROM MyTable t1
INNER JOIN MyTable t2
WHERE t1.RowID > t2.RowID
  AND t1.Col1 = t2.Col1
  AND t1.Col2=t2.Col2
  AND t1.Col3=t2.Col3;

我假设RowID是一种自动递增,其余列有重复的值。

DELETE
FROM
    table_name T1
WHERE
    rowid > (
        SELECT
            min(rowid)
        FROM
            table_name T2
        WHERE
            T1.column_name = T2.column_name
    );
DELETE LU 
FROM   (SELECT *, 
               Row_number() 
                 OVER ( 
                   partition BY col1, col1, col3 
                   ORDER BY rowid DESC) [Row] 
        FROM   mytable) LU 
WHERE  [row] > 1 

我想我应该分享我的解决方案,因为它在特殊情况下是有效的。 在我的例子中,有重复值的表没有外键(因为这些值是从另一个db复制的)。

begin transaction
-- create temp table with identical structure as source table
Select * Into #temp From tableName Where 1 = 2

-- insert distinct values into temp
insert into #temp 
select distinct * 
from  tableName

-- delete from source
delete from tableName 

-- insert into source from temp
insert into tableName 
select * 
from #temp

rollback transaction
-- if this works, change rollback to commit and execute again to keep you changes!!

PS:在处理这样的事情时,我总是使用事务,这不仅确保了所有事情都作为一个整体执行,而且还允许我在没有任何风险的情况下进行测试。但是当然你应该做个备份,以防万一……