SQLSQL 删除重复记录删除重复记录-如何按字段删除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，需要删除重复项，如下表a b c d1 2 3 41 5 3 51 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 d1 2 3 41 5 3 5或a b c d1 5 3 51 2 7 9请问各位大侠这种 sql 语句怎么写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, 1,2,3,4UNION ALL SELECT 2, 1,5,3,5UNION ALL SELECT 3, 1,2,7,9UNION ALL SELECT 4, 1,4,7,6delete Tb1 where id not in (select max(id) from Tb1 group by a,b )select * from tb1drop table tb1如果要同时删除第一和第三行即如下结果：a b c d1 5 3 5语句如下：delete m from tb tinner join(select a ,bfrom tbgroup by a , bhaving count(*)1)non m.a = n.a and m.b = n.b 或delete * from tb as m,(select a ,bfrom tbgroup by a , bhaving count(*)1)nwhere 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?谢谢!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 peoplewhere 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 awhere (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 awhere (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 awhere (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)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-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）select * from tablename where id in (select id from tablename group by id having count(id) 1)-先找出重复记录 插入到临时表中 insert into #temp select col1,col2. from table group by col1,col2. having count(*)1 -删除这些重复记录 delete table from #temp where table.col1=#temp.col1 and table.col2=#temp.col2. -再将临时表的数据反添回来 insert into table select col1,col2 .from #temp