Oracle查询重复数据与删除重复数据
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一、Oracle查询重复数据:
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比如现在有一人员表 (表名:peosons),若想将姓名、身份证号、住址这三个字段完全相同的记录查询出来
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select p1.*
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from persons p1,persons p2
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where p1.id<>p2.id
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and p1.cardid = p2.cardid and p1.pname = p2.pname and p1.address = p2.address
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可以实现上述效果。
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二、Oracle删除重复数据
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几个删除重复记录的SQL语句
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1.用rowid方法
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2.用group by方法
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3.用distinct方法
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1。用rowid方法
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据据oracle带的rowid属性,进行判断,是否存在重复,语句如下:
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查数据:
select * from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=b.name2……)
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删数据:
delete from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=b.name2……)
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2.group by方法
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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
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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。
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3.用distinct方法 -对于小的表比较有用
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create table table_new as select distinct * from table1 minux
truncate table table1;
insert into table1 select * from table_new;
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三、
查询及删除重复记录的方法大全
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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
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select * from people
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where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
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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
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delete from people
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where peopleId in (select peopleId from people group by peopleId
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having count(peopleId) > 1)
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and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
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3、查找表中多余的重复记录(多个字段)
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select * from vitae a
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where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
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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
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delete from vitae a
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where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
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and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
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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
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select * from vitae a
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where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
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and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
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(二)
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比方说
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在A表中存在一个字段“name”,
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而且不同记录之间的“name”值有可能会相同,
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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;
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Select Name,Count(*) From A Group By Name Having Count(*) > 1
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如果还查性别也相同大则如下:
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Select Name,***,Count(*) From A Group By Name,*** Having Count(*) > 1
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(三)
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方法一
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declare @max integer,@id integer
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declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1
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open cur_rows
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fetch cur_rows into @id,@max
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while @@fetch_status=0
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begin
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select @max = @max -1
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set rowcount @max
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delete from 表名 where 主字段 = @id
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fetch cur_rows into @id,@max
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end
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close cur_rows
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set rowcount 0
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方法二
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"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,
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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。
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1、对于第一种重复,比较容易解决,使用
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select distinct * from tableName就可以得到无重复记录的结果集。
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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
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select distinct * into #Tmp from tableName
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drop table tableName
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select * into tableName from #Tmp
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drop table #Tmp
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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。
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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
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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
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select identity(int,1,1) as autoID, * into #Tmp from tableName
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select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
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select * from #Tmp where autoID in(select autoID from #tmp2)
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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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(四)
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查询重复
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select * from tablename where id in (
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select id from tablename
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group by id
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having count(id) > 1
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)
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