SQL查詢重複記錄

假設現有一張人員表（表名：Person），若想將姓名、身份證號、住址這三個字段完全相同的記錄查找出來，使用

  1: SELECT p1.*   

  2: FROM persons   p1,persons   p2   

  3: WHERE p1.id<>p2.id   

  4: AND p1.cardid   =   p2.cardid   

  5: AND p1.pname   =   p2.pname   

  6: AND p1.address   =   p2.address

可以實現該功能。

刪除重複記錄的SQL語句

1.用rowid方法

2.用group by方法

3.用distinct方法

1。用rowid方法

據據oracle帶的rowid屬性，進行判斷，是否存在重複,語句如下：
查數據:
select * from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=b.name2......)
刪數據：
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

查數據:
select count(num), max(name) from student --列出重複的記錄數，並列出他的name屬性
group by num
having count(num) >1 --按num分組後找出表中num列重複，即出現次數大於一次
刪數據：
delete from student
group by num
having count(num) >1
這樣的話就把所有重複的都刪除了。

3.用distinct方法 -對於小的表比較有用

create table table_new as select distinct * from table1 minux
truncate table table1;
insert into table1 select * from table_new;

查詢及刪除重複記錄的方法大全
1、查找表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷

select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

2、刪除表中多餘的重複記錄，重複記錄是根據單個字段（peopleId）來判斷，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)

3、查找表中多餘的重複記錄（多個字段）
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

4、刪除表中多餘的重複記錄（多個字段），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、查找表中多餘的重複記錄（多個字段），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 在A表中存在一個字段“name”，
而且不同記錄之間的“name”值有可能會相同，
現在就是需要查詢出在該表中的各記錄之間，“name”值存在重複的項；
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

＂重複記錄＂有兩個意義上的重複記錄，一是完全重複的記錄，也即所有字段均重複的記錄，二是部分關鍵字段重複的記錄，比如Name字段重複，而其他字段不一定重複或都重複可以忽略。

1、對於第一種重複，比較容易解決，使用

select distinct * from tableName

就可以得到無重複記錄的結果集。

如果該表需要刪除重複的記錄（重複記錄保留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

發生這種重複的原因是表設計不周產生的，增加唯一索引列即可解決。

2、這類重複問題通常要求保留重複記錄中的第一條記錄，操作方法如下

假設有重複的字段爲Name,Address，要求得到這兩個字段唯一的結果集

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)

最後一個select即得到了Name，Address不重複的結果集（但多了一個autoID字段，實際寫時可以寫在select子句中省去此列）

(四) 查詢重複

select * from tablename where id in (

select id from tablename

group by id

having count(id) > 1)