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)
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
2.group by方法
查数据:
select count(num), max(name) from student --列出重复的记录数，并列出他的name属性
group by num
having count(num) >1 --按num分组后找出表中num列重复，即出现次数大于一次
删数据：
delete from student
group by num
having count(num) >1
这样的话就把所有重复的都删除了。
3.用distinct方法 -对于小的表比较有用
create table table_new as select distinct * from table1 minux
truncate table table1;
insert into table1 select * from table_new;
delete select a.* from FLRK1 a inner join FLRK1 b on a.记录号=b.记录号 and
(a.[ID]=b.[ID] and a.入库日期=b.入库日期 and a.操作时间=b.操作时间)
delete from FLRK1 where 记录号 in
(select min(记录号) from FLRK1 group by 记录号 having count(记录号)>1)
A表结构：
ID RQ SJ C
--------------------------------------------
1 2005-07-14 14:20:50 A1
2 2005-02-15 05:12:23 A1
3 2005-07-14 14:20:50 A1
4 2005-06-16 16:16:16 A2
5 2005-06-16 16:16:16 A2
6 2005-05-18 05:10:35 A3
7 2005-02-15 05:12:23 A1
--------------------------------------------
求SQL语句一条，把表A中 RQ,SJ,C 三个字段有相同的重复记录删除．
得到的结果：
ID RQ SJ C
--------------------------------------------
1 2005-07-14 14:20:50 A1
2 2005-02-15 05:12:23 A1
4 2005-06-16 16:16:16 A2
6 2005-05-18 05:10:35 A3
--------------------------------------------
Delete from A Where ID Not In (Select Min(ID) from A Group By RQ,SJ,C )
Delete a from tb a inner join tb as b on a.fid<b.fid and a.c=b.c and a.rq=b.rq and a.sj=b.sj
delete from A t
where exists(select 1 from A where ID<A.ID and SJ=t.SJ and RQ=t.RQ and C=t.c)
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
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）
