SQL查出一张表中重复的所有记录数据
1、在面试的时候碰到一个 问题,就是让写一张表中有id和name 两个字段,查询出name重复的所有数据,现在列下:
SELECT * from xi a where (a.username) in (SELECT username from xi group by username having count(*) > 1)
2、查询出所有数据进行分组之后,和重复数据的重复次数的查询数据,先列下:
SELECT count(username) as '重复次数',username from xi group by username having count(*)>1 order by username desc
3、一下为 查看别人的 结果,现列下: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)
另外,MySQL中使用上面的SQL会报错:You can't specify target table 'XXX' for update in FROM clause,不能在修改表的同时去查询同一张表,因此可以像下面的语句一样,将查询结果命名为一张临时表来作为修改表数据的条件,以规避上述错误。
DELETE from user where user_id in( (SELECT user_id from (SELECT c.* from cab_user c where c.extra_id in (SELECT a.extra_id from user a group by a.extra_id having count(a.extra_id) > 1) and c.user_id not in (SELECT min(b.user_id) from user b group by b.extra_id having count(b.extra_id )>1) ) d ) )
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 integerdeclare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >; 1open cur_rowsfetch cur_rows into @id,@maxwhile @@fetch_status=0beginselect @max = @max -1set rowcount @maxdelete from 表名 where 主字段 = @idfetch cur_rows into @id,@maxendclose cur_rowsset 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 tableNamedrop table tableNameselect * into tableName from #Tmpdrop 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 tableNameselect min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoIDselect * 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 tablenamegroup by idhaving count(id) > 1)

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