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Possible Duplicate:
delete duplicate records in SQL Server
我有一个表，其中唯一记录由复合键表示，例如 (COL_A, COL_B)。
我已使用以下查询检查并确认我的表中有重复行:
select COL_A, COL_B, COUNT(*)
from MY_TABLE
group by COL_A, COL_B
having count(*) > 1
order by count(*) desc
现在，我想删除所有重复的记录，但只保留一个。
有人可以阐明如何使用 2 列实现这一目标吗？
编辑:
假设表格只有 COL_A 和 COL_B
最佳答案
第一个解决方案，
它很灵活，因为您可以添加比 COL_A 和 COL_B 更多的列:
-- create table with identity filed
-- using idenity we can decide which row we can delete
create table MY_TABLE_COPY
(
id int identity,
COL_A varchar(30),
COL_B varchar(30)
/*
other columns
*/
)
go
-- copy data
insert into MY_TABLE_COPY (COL_A,COL_B/*other columns*/)
select COL_A, COL_B /*other columns*/
from MY_TABLE
group by COL_A, COL_B
having count(*) > 1
-- delete data from MY_TABLE
-- only duplicates (!)
delete MY_TABLE
from MY_TABLE_COPY c, MY_TABLE t
where c.COL_A=t.COL_A
and c.COL_B=t.COL_B
go
-- copy data without duplicates
insert into MY_TABLE (COL_A, COL_B /*other columns*/)
select t.COL_A, t.COL_B /*other columns*/
from MY_TABLE_COPY t
where t.id = (
select max(id)
from MY_TABLE_COPY c
where t.COL_A = c.COL_A
and t.COL_B = c.COL_B
)
go
第二种解决方案 如果您在 MY_TABLE 中确实有两列，您可以使用:
-- create table and copy data
select distinct COL_A, COL_B
into MY_TABLE_COPY
from MY_TABLE
-- delete data from MY_TABLE
-- only duplicates (!)
delete MY_TABLE
from MY_TABLE_COPY c, MY_TABLE t
where c.COL_A=t.COL_A
and c.COL_B=t.COL_B
go
-- copy data without duplicates
insert into MY_TABLE
select t.COL_A, t.COL_B
from MY_TABLE_COPY t
go
关于SQL查询删除所有重复记录，但一个，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12939893/