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qy1.Open "select distinct xsrq from xszb ", cnn, adOpenStatic, adLockReadOnly, adCmdText

怎么提示记录为空啊
答案: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

一。查找重复记录

1。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)

2。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

二。删除重复记录


1。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)

2。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

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)


补充:

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。



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)
其他:distinct 后面加任何数字结果都是1,为什么? distinct 去重后再进行count 求条数,结果当然是1了,因为distinct -1.2表示去除表中所有重复的为-1.2 

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