查重 查重复记录 删除重复记录

Posted 2020-08-30 我为卒

 select * from b;
 
        ID        AID NAME
---------- ---------- --------------------------------------------------------------------------------
         1          1 b1
         2          2 b2
         3          2 b2
         4          2 b3
 

　　

这是表的记录   :

 

 

--根据 aid 和 name 进行同时查询 :

--第一种

select * from b  b1 where exists ( select 1 from b b2 where b1.aid=b2.aid and b1.name=b2.name group by b2.aid,b2.name  having count(1)>1);
 

 

 

 

 

--第二种

 

select b1.* from b b1,b b2 where b1.aid=b2.aid and b1.name=b2.name and b1.id<>b2.id;
 

　　

 

 

--第三种

select * from b b1 where b1.aid in( select aid from b b2  group by b2.aid,b2.name  having count(1)>1) and b1.name in(select name from b b2  group by b2.aid,b2.name  having count(1)>1);

--上面可以优化 

select * from b b1 where (b1.aid,b1.name) in( select aid,name from b b2  group by b2.aid,b2.name  having count(1)>1);

　　

 

--如果只是根据一个字段进行查询呢 上面的进行修改,应该很简单了 为什么第一个sql 中要查询1 呢 效率上 1>aid>* exits 里面只是true或者false 所以查询什么都可以

 

 

 

下面是网上摘抄的 没有进行验证的  : 可以参考

 

- 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

- select p1.* from persons p1,persons p2 where p1.id<>p2.id and p1.cardid = p2.cardid and p1.pname = p2.pname and p1.address = p2.address

-

- 可以实现上述效果．

-

- 几个删除重复记录的SQL语句

-

- 1.用rowid方法

-

- 2.用group by方法

-

- 3.用distinct方法

-

-

- 1。用rowid方法

-

- 据据Oracle带的rowid属性，进行判断，是否存在重复,语句如下：

- 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......)

- 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......)

-

- 2.group by方法

-

- 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

- 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。

-

- 3.用distinct方法 -对于小的表比较有用

-

- create table table_new as select distinct * from table1 minux

- truncate table table1;

- insert into table1 select * from table_new;

-

-

-

- 查询及删除重复记录的方法大全

-

- 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

- ＂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 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

- )