SQL-删除重复数据
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例.
id name value
1 a pp
2 a pp
3 b iii
4 b pp
5 b pp
6 c pp
7 c pp
8 c iii
id是主键
1.要求得到如下结果:
id name value
2app3biii5bpp7cpp8ciii方法
delete YourTable
where [id] not in (
select max([id]) from YourTable
group by (name + value))
2.要求得到如下结果
id name value
1 a pp
3 b iii
4 b pp
6 c pp
8 c iii
方法
delete a
from 表 a left join(
select id=min(id) from 表 group by name,value
)b on a.id=b.id
where b.id is null
查询及删除重复记录的SQL语句
"重复记录"有两个意义上,一是完全重复的记录,也即所有字段均重复的记录,
二是部分关键字段重复的记录,比如Name字段重复,而其他字段不一定重复或都重复可以忽略。
(一)第一种重复,可使用如下语句得到无重复记录的结果集:
select distinct * from tableName
发生这种重复的原因是表设计不周产生的,增加唯一索引列即可解决【待验证】。
(二)第二种重复:
1、查找表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断
select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、删除表中多余的重复记录,重复记录是根据单个字段(peopleId)来判断,只留有rowid最小的记录
delete from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
3、查找表中多余的重复记录(多个字段)
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
4、删除表中多余的重复记录(多个字段),只留有rowid最小的记录
delete from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
5、查找表中多余的重复记录(多个字段),不包含rowid最小的记录
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
6、在A表中存在一个字段“name”,且不同记录之间的“name”值有可能会相同,
查询出在该表中的各记录之间,“name”值存在重复的项:
Select Name,Count(*) From A Group By Name Having Count(*) > 1
如果还查性别也相同,则如下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
(三) 【待验证】
方法一
declare @max integer,@id integer
declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1
open cur_rows
fetch cur_rows into @id,@max
while @@fetch_status=0
begin
select @max = @max -1
set rowcount @max
delete from 表名 where 主字段 = @id
fetch cur_rows into @id,@max
end
close cur_rows
set rowcount 0
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