蚂蚁
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)
delete 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。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
delete #temp
where id not in
(
select max(id) from # group by col1,col2,col3...
)
delete table ta
inset into ta(...)
select ..... from #tempb: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
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)
delete 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。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
delete #temp
where id not in
(
select max(id) from # group by col1,col2,col3...
)
delete table ta
inset into ta(...)
select ..... from #tempb: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
select distinct * into #temp from 表
go
truncate table 表
go
insert 表
select * from #temp
go
drop table #temp
go
where id not in
(
select max(id) from table group by col1,col2,col3...
)
1 as
3 g
4 k
5 g
1 as
下面是sql
select distinct * into temptable1 from table2
truncate table table2
insert into table2 select * from temptable1
drop table temptable1
select * from table2----------测试结果-------------
1 as
3 g
4 k
5 g
--------------------------------(所影响的行数为 4 行)
(所影响的行数为 4 行)
(所影响的行数为 4 行)