如何删除SQLServer表中重复记录
一张表里面以两个字段为唯一字段,当几条记录的这两个字段完全相同时,即出现重复记录,需要删除重复项,如下面表: a b c d 1 2 3 4 1 5 3 5 1 2 7 9
create table tb(a int,b int,c int,d int) insert into tb select 1,2,3,4 union all select 1,5,3,5 union all select 1,2,7,9 以a、b为唯一字段,第一条和第三条的a、b完全相同,所以,需要删除第一条记录1 2 3 4 或者第三条记录1 2 7 9 即如下结果: a b c d 1 2 3 4 1 5 3 5 或 a b c d 1 5 3 5 1 2 7 9
SQL语句如下
CREATE TABLE Tb1(id int, [a] varchar(255), [b] varchar(255), [c] varchar(255), [d] varchar(255)) INSERT Tb1(id, [a], [b], [c], [d]) SELECT 1, '1','2','3','4' UNION ALL SELECT 2, '1','5','3','5' UNION ALL SELECT 3, '1','2','7','9' UNION ALL SELECT 4, '1','4','7','6'
del ete Tb1 where [id] not in (sel ect max([id]) fro m Tb1 group by a,b ) sel ect * fro m tb1 drop table tb1
如果要同时删除第一和第三行 即如下结果: a b c d 1 5 3 5
语句如下:
delete * from tb t inner join ( select a ,b from tb group by a , b having count(*)>1 )n on t.a = n.a and t.b = n.b 或 delete tb from tb m, ( select a ,b from tb group by a , b having count(*)>1 ) n where m.a = n.a and m.b = n.b
在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢? 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 sel ect * fro m people where peopleId in (sel ect peopleId fro m 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 del ete fro m people where peopleId in (sel ect peopleId fro m people group by peopleId having count(peopleId) > 1) and rowid not in (sel ect min(rowid) fro m people group by peopleId having count(peopleId )>1)
3、查找表中多余的重复记录(多个字段) sel ect * fro m vitae a where (a.peopleId,a.seq) in (sel ect peopleId,seq fro m 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 del ete fro m vitae a where (a.peopleId,a.seq) in (sel ect peopleId,seq fro m vitae group by peopleId,seq having count(*) > 1) and rowid not in (sel ect min(rowid) fro m 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 sel ect * fro m vitae a where (a.peopleId,a.seq) in (sel ect peopleId,seq fro m vitae group by peopleId,seq having count(*) > 1) and rowid not in (sel ect min(rowid) fro m vitae group by peopleId,seq having count(*)>1)
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,--,Count(*) From A Group By Name,-- Having Count(*) > 1 ------------------------------------------------------------------------------------------------ declare @max integer,@id integer declare cur_rows cursor local for sel ect 主字段,count(*) fro m 表名 group by 主字段 having count(*) >; 1 open cur_rows fetch cur_rows into @id,@max while @@fetch_status=0 begin sel ect @max = @max -1 set rowcount @max del ete fro m 表名 where 主字段 = @id fetch cur_rows into @id,@max end close cur_rows set rowcount 0
方法二 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 sel ect distinct * fro m 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 sel ect distinct * into #Tmp fro m tableName drop table tableName sel ect * into tableName fro m #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 sel ect identity(int,1,1) as autoID, * into #Tmp fro m tableName sel ect min(autoID) as autoID into #Tmp2 fro m #Tmp group by Name,autoID sel ect * fro m #Tmp where autoID in(sel ect autoID fro m #tmp2) 最后一个sel ect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sel ect子句中省去此列) sel ect * fro m tablename where id in ( sel ect id fro m tablename group by id having count(id) > 1)
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