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sql重复记录查询与删除

 
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mysql> create temporary table tmp_wrap select * from users_groups group by uid having count(1) >= 1;
Query OK, 7 rows affected (0.11 sec)
Records: 7  Duplicates: 0  Warnings: 0

mysql> truncate table users_groups;
Query OK, 14 rows affected (0.03 sec)

mysql> insert into users_groups select * from tmp_wrap;
Query OK, 7 rows affected (0.03 sec)
Records: 7  Duplicates: 0  Warnings: 0

 

 

=== 下面的方法,执行时间特别长,可能是由 "in" 的关系,慎用

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
)
(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   - 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)

(四) 查询重复
select   *   from  tablename  where  id  in
 (
select  id  from
 tablename 
group   by
 id 
having   count (id)  >   1

)

 

转载自iteye:http://h819.iteye.com/blog/531197

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