查詢及刪除重復(fù)記錄的SQL語(yǔ)句
1、查找表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（peopleId）來(lái)判斷
select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、刪除表中多余的重復(fù)記錄，重復(fù)記錄是根據(jù)單個(gè)字段（peopleId）來(lái)判斷，只留有rowid最小的記錄
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)
注:rowid為Oracle自帶不用該.....
3、查找表中多余的重復(fù)記錄（多個(gè)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、刪除表中多余的重復(fù)記錄（多個(gè)字段），只留有rowid最小的記錄
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、查找表中多余的重復(fù)記錄（多個(gè)字段），不包含rowid最小的記錄
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)
(二)
比方說(shuō)在A表中存在一個(gè)字段“name”，而且不同記錄之間的“name”值有可能會(huì)相同，
現(xiàn)在就是需要查詢出在該表中的各記錄之間，“name”值存在重復(fù)的項(xiàng)；
Select Name,Count(*) From A Group By Name Having Count(*) > 1
如果還查性別也相同大則如下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
(三)
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
方法二
＂重復(fù)記錄＂有兩個(gè)意義上的重復(fù)記錄，一是完全重復(fù)的記錄，也即所有字段均重復(fù)的記錄，二是部分關(guān)鍵字段重復(fù)的記錄，比如Name字段重復(fù)，而其他字段不一定重復(fù)或都重復(fù)可以忽略。
1、對(duì)于第一種重復(fù)，比較容易解決，使用
select distinct * from tableName
就可以得到無(wú)重復(fù)記錄的結(jié)果集。 如果該表需要?jiǎng)h除重復(fù)的記錄（重復(fù)記錄保留1條），可以按以下方法刪除
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
發(fā)生這種重復(fù)的原因是表設(shè)計(jì)不周產(chǎn)生的，增加唯一索引列即可解決。
2、這類重復(fù)問(wèn)題通常要求保留重復(fù)記錄中的第一條記錄，操作方法如下
假設(shè)有重復(fù)的字段為Name,Address，要求得到這兩個(gè)字段唯一的結(jié)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)
最后一個(gè)select即得到了Name，Address不重復(fù)的結(jié)果集（但多了一個(gè)autoID字段，實(shí)際寫時(shí)可以寫在select子句中省去此列）
(四)
查詢重復(fù)
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1)
=======================================
1。用rowid方法
據(jù)據(jù)Oracle帶的rowid屬性，進(jìn)行判定，是否存在重復(fù),語(yǔ)句如下：
查數(shù)據(jù):
select * from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=b.name2......)
刪數(shù)據(jù)：
delete from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=b.name2......)
2.group by方法
查數(shù)據(jù):
select count(num), max(name) from student --列出重復(fù)的記錄數(shù)，并列出他的name屬性
group by num
having count(num) >1 --按num分組后找出表中num列重復(fù)，即出現(xiàn)次數(shù)大于一次
刪數(shù)據(jù)：
delete from student
group by num
having count(num) >1
這樣的話就把所有重復(fù)的都刪除了。
3.用distinct方法 -對(duì)于小的表比較有用
create table table_new as select distinct * from table1 minux
truncate table table1;
insert into table1 select * from table_new;
