SQL删除、查找重复数据记录等操作-mysql教程

数据库产生重复数据记录是经常发生的事情，现在NowaMagic总结下各种重复的情况，每一种情况该如何写SQL语句处理。 查找所有重复标题的记录： SELECT *FROM t_info aWHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1)ORDER BY Title DESC 查

数据库产生重复数据记录是经常发生的事情，现在NowaMagic总结下各种重复的情况，每一种情况该如何写SQL语句处理。

查找所有重复标题的记录：

SELECT *
FROM t_info a
WHERE ((SELECT COUNT(*)
          FROM t_info
          WHERE Title = a.Title) > 1)
ORDER BY Title DESC

查找全部重复记录：

Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)

过滤重复记录（只显示一条）：

Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)

注：此处显示ID最大一条记录。

删除全部重复记录（慎用）：

Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)

保留一条（这个应该是大多数人所需要的 ^_^）：

Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)

注：此处保留ID最大一条记录。

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)

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)

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)

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)

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)

有两个以上的重复记录，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。

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。

第二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)