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如何删除表中的重复记录只保留其中一条

如何删除表中的重复记录只保留其中一条
 
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,易做图,Count(*) From A Group By Name,易做图 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
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