1.表中有id和name 两个字段，查询出name重复的所有数据
| 1 | 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：
| 1 | 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
| 1 2 | 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
| 1 2 3 | 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）
| 1 2 | 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
| 1 2 3 | 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
| 1 2 3 | 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；
| 1 | Select Name , Count (*) From A Group By Name Having Count (*) > 1 |
如果还查性别也相同大则如下:
| 1 | Select Name ,sex, Count (*) From A Group By Name ,sex Having Count (*) > 1 |
(三)
方法一
| 1 2 3 4 5 6 7 8 9 10 11 | 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 (*) >; open cur_rows fetch cur_rows into @id,@maxwhile @@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,@maxend 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
| 1 | 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
| 1 2 3 4 | 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
| 1 2 3 | 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
| 1 | select * from tablename where id in ( select id from tablenamegroup by idhaving count (id) > 1) |
对一个字段查找重复记录
根据sample_code字段找到重复记录
| 1 | SELECT * FROM tb_table WHERE sample_code IN ( SELECT sample_code FROM tb_table GROUP BY sample_code HAVING COUNT (sample_code) > 1 ); |
对多个字段查找重复记录（这里以2个为例）
根据name和code字段找到重复记录
| 1 2 3 4 | SELECT * from ( SELECT *, CONCAT( name ,code) as nameAndCode from tb_table) t WHERE t.nameAndCode in ( SELECT nameAndCode from ( SELECT CONCAT( name ,code) as nameAndCode from tb_table) tt GROUP BY nameAndCode HAVING count (nameAndCode) > 1 ) |