经典SQL语句大全之重复记录篇
2011-04-15
数据库的重复记录有两种概念：
1> 完全重复的记录，即所有字段均重复的记录
2> 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
二、删除重复记录
1> 完全重复的记录，即所有字段均重复的记录
2> 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
一、查询重复记录
1、过滤掉完全重复的记录（即字段完全重复时只取其中一条）
select distinct 字段1,字段2,字段3 from 数据表
2、过滤部分关键字段重复的记录
数据结构：角色档案（角色编码，角色，角色分类编码）
功 能：取出指定字段（角色分类编码）为关键字的无重复数据，重复的取第一条
说 明：重复记录取最后一条，只需要把min改成max即可
select * from 角色档案 t where 角色编码 in (select min(角色编码) from 角色档案 t1 group by t1.角色分类编码)
二、删除重复记录
数据库的使用过程中由于程序方面的问题有时候会碰到重复数据，本例举出删除它的办法。
删除重复记录方法一
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(*) > 1
open cur_rows
fetch cur_rows into @id,@max
while @@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,@max
end
close cur_rows
set rowcount 0
declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) > 1
open cur_rows
fetch cur_rows into @id,@max
while @@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,@max
end
close cur_rows
set rowcount 0
删除重复记录方法二
1、删除完全重复的记录
select distinct * from tableName
以上语句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
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
发生这种重复的原因可能是表没有设计唯一索引列。
2、删除部分关键字段重复的记录，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)
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）。
三 采用Having关键字处理SQL查询重复记录的语句
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)
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)
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)
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)
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)
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)
6> 删除重复记录
delete from 表名 where (重复字段1，重复字段2，……)
in ( select 重复字段1，重复字段2，…… from 表名 group by 重复字段1，重复字段2，…… having count(*) >1)
and 主键 not in (
select 主键 from
(select 主键 ,row_number() over(partition by 重复字段1，重复字段2，…… order by 重复字段1，重复字段2，……) rownum from 表名
where (重复字段1，重复字段2，……) in (
select 重复字段1，重复字段2，…… from 表名 group by 重复字段1，重复字段2，……
having count(*) >1))
where rownum =1)
in ( select 重复字段1，重复字段2，…… from 表名 group by 重复字段1，重复字段2，…… having count(*) >1)
and 主键 not in (
select 主键 from
(select 主键 ,row_number() over(partition by 重复字段1，重复字段2，…… order by 重复字段1，重复字段2，……) rownum from 表名
where (重复字段1，重复字段2，……) in (
select 重复字段1，重复字段2，…… from 表名 group by 重复字段1，重复字段2，……
having count(*) >1))
where rownum =1)
