SQL查询重复数据
1、查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 havingcount(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
(⼆)
⽐⽅说在A表中存在⼀个字段“name”，⽽且不同记录之间的“name”值有可能会相同，现在就是需要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⼤则如下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
(三)
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 -1delete in
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
⽅法⼆
有两个意义上的重复记录，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。
  1、对于第⼀种重复，⽐较容易解决，使⽤  select distinct * from tableName  就可以得到⽆重复记录的结果集。
如果该表需要删除重复的记录（重复记录保留1条），可以按以下⽅法删除
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
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。
　2、这类重复问题通常要求保留重复记录中的第⼀条记录，操作⽅法如下
  假设有重复的字段为Name,Address，要求得到这两个字段唯⼀的结果集
select identity(int,1,1) as autoID, * into #Tmp from tableName
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
select * from #Tmp where autoID in(select autoID from #tmp2)
最后⼀个select即得到了Name，Address不重复的结果集（但多了⼀个autoID字段，实际写时可以写在select⼦句中省去此列）(四)查询重复
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1
)