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一个表有多条纪录出主键外其他字段的值都相同,怎样消除这样的重复记录?
如 tb_mytable
tb_id(主键) field1, filed2
1 a1 b1
2 a2 b2
3 a2 b2
4 a3 b3
我想要的纪录为
1 a1 b1
3 a2 b2
4 a3 b3
注:重复纪录中取tb_id最大的
select * from tb_mytable 别名 where tb_id=(select max(tb_id) from tb_mytable where field1=别名.field1 and field2=别名.field2)
delete tb_mytable
where tb_id not in
(select tb_id from tb_mytable a where tb_id=(select max(tb_id) from tb_mytable
where field1=a.field1 and field2=a.field2)
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
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
delete from tb_mytable
where tb_id not in
(
select max(tb_id) from tb_mytable group by field1 ,filed2
)
