SQL查询重复记录

左手的ㄟ右手 2022-08-10 15:00 217阅读 0赞

假设现有一张人员表（表名：Person），若想将姓名、身份证号、住址这三个字段完全相同的记录查找出来，使用

1:  SELECT p1.*

2:  FROM persons   p1,persons   p2

3:  WHERE p1.id<>p2.id

4:  AND p1.cardid   =   p2.cardid

5:  AND p1.pname   =   p2.pname

6:  AND p1.address   =   p2.address

可以实现该功能。

> **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)