找出相同记录并删除的剩下唯一一个？
---------------------------------------------------------------
select distinct * into #temp from 表
truncate table 表
insert 表 select * from #temp
drop table #temp
---------------------------------------------------------------
alter table 表 add newfield int identity(1,1)
delete 表
where newfield not in(
select min(newfield) from 表 group by 除newfield外的所有字段
)
alter table 表 drop column newfield
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删除重复数据
一、具有主键的情况
a.具有唯一性的字段id(为唯一主键)
delect table
where id not in
(
select max(id) from table group by col1,col2,col3...
)
group by 子句后跟的字段就是你用来判断重复的条件，如只有col1，
那么只要col1字段内容相同即表示记录相同。
b.具有联合主键
假设col1+','+col2+','...col5 为联合主键
select * from table where col1+','+col2+','...col5 in (
select max(col1+','+col2+','...col5) from table
where having count(*)>1
group by col1,col2,col3,col4
)
group by 子句后跟的字段就是你用来判断重复的条件，
如只有col1，那么只要col1字段内容相同即表示记录相同。
or
select * from table where exists (select 1 from table x where table.col1 = x.col1 and
table.col2= x.col2 group by x.col1,x.col2 having count(*) >1)
c:判断所有的字段
select * into #aa from table group by id1,id2,....
delete table
insert into table
select * from #aa
二、没有主键的情况
a:用临时表实现
select identity(int,1,1) as id,* into #temp from ta
delect #temp
where id not in
(
select max(id) from # group by col1,col2,col3...
)
delete table ta
inset into ta(...)
select ..... from #temp
b:用改变表结构（加一个唯一字段）来实现
alter table 表 add newfield int identity(1,1)
delete 表
where newfield not in
(
select min(newfield) from 表 group by 除newfield外的所有字段
)
alter table 表 drop column newfield