sql去重查询的方法：

sql 单表/多表查询去除重复记录

单表distinct

多表group by

group by 必须放在 order by 和 limit之前，不然会报错

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 peoplewhere 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 peoplewhere 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 awhere (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 awhere (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 awhere (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)

(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 integerdeclare cur_rows cursor local for ｓｅｌｅｃｔ 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1open cur_rowsfetch cur_rows into @id,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @idfetch cur_rows into @id,@maxendclose cur_rowsset rowcount 0

方法二

＂重复记录＂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 tableNamedrop table tableNameselect * into tableName from #Tmpdrop 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 tableNameselect min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoIDselect * 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 tablenamegroup by idhaving count(id) > 1)

3、查找表中多余的重复记录（多个字段）

ｓｅｌｅｃｔ * from vitae awhere (a.peopleId,a.seq) in (ｓｅｌｅｃｔ peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

运行会产生问题，where(a.peopleId,a.seq)这样的写发是通不过的！！！