转载http://hi.baidu.com/my_favourate/item/3716b0cbe125f312505058eb
由于设计需要，需要查询不重复的记录值，同类问题，想必大家都遇到过，于是乎马上GOOGLE一下，发现此类问题还挺多，解决方案也不少，仔细看看。
例如有如下表结构和值
table
fid name sex
1 a 男
2 b 男
3 c 女
4 d 女
5 a 男
6 b 男
方案一：distinct
select distinct name from table
得到结果：
name
a
b
c
d
实现效果，那如果要同时打开其它记录呢？再试试
select distinct name,id from table
测试没什么效果，查下得知，这样实际是要name和id字段都重复才被筛选。继续查找可得如下方法：
方案二：group by
select *, count(distinct name) from table group by name
Oracle下测试失败，据说MYSQL下通过，不管，继续思考....
翻翻书，试试
select min(fid),name,sex from table group by name
成功，现实如下结果：
fid name sex
1 a 男
2 b 男
3 c 女
4 d 女
继续思考，如果要打开所有记录，不指定字段用（*），貌似这方法就不行了！
select * from table where fid in(Select min(fid) FROM table group by name)
测试成功
fid name sex
1 a 男
2 b 男
3 c 女
4 d 女
方案三：
本来已经完了，突然想起前几天在网上查了查询数据中所有某字段重复的记录
select * from table where name in(select name from table group by name having count(name)=2)
得到如下结果：
fid name sex
1 a 男
2 b 男
5 a 男
6 b 男
以此类推：
select * from table where name in(select name from table group by name having count(name)=1)
按道理说没问题，大家试试~~
再多的字段都全部现实。哎，原来如此简单！回顾网上方法distinct，Inner Join等等，麻烦，而且有很大局限性.
总结如下：
select distinct name from table打开重复记录的单个字段
select * from table where fid in(Select min(fid) FROM table group by name)打开重复记录的所有字段值
select * from table where name in(select name from table group by name having count(name)=1)打开重复任意次数的所有记录
在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢?谢谢!
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