MySQL查询及删除重复记录的方法

查询及删除重复记录的方法
(一)
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
);

from http://www.zhaipeng.cn/2009/05/14/mysql%E6%9F%A5%E8%AF%A2%E5%8F%8A%E5%88%A0%E9%99%A4%E9%87%8D%E5%A4%8D%E8%AE%B0%E5%BD%95%E7%9A%84%E6%96%B9%E6%B3%95/



coded by nessus
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