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
- )