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例如：

id name value

1 a pp

2 a pp

3 b iii

4 b pp

5 b pp

6 c pp

7 c pp

8 c iii

id是主鍵

要求得到這樣的結(jié)果

id name value

1 a pp

3 b iii

4 b pp

6 c pp

8 c iii

方法1

delete YourTable

where [id] not in (

select max([id]) from YourTable

group by (name + value))

方法2

delete a

from 表 a left join(

select id=min(id) from 表 group by name,value

)b on a.id=b.id

where b.id is null

查詢及刪除重復(fù)記錄的SQL語句

查詢及刪除重復(fù)記錄的SQL語句

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

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

)

學(xué)習(xí)sql有一段時(shí)間了，發(fā)現(xiàn)在我建了一個(gè)用來測(cè)試的表(沒有建索引)中出現(xiàn)了許多的重復(fù)記錄。后來總結(jié)了一些刪除重復(fù)記錄的方法，在Oracle中，可以通過唯一rowid實(shí)現(xiàn)刪除重復(fù)記錄;還可以建臨時(shí)表來實(shí)現(xiàn)...這個(gè)只提到其中的幾種簡(jiǎn)單實(shí)用的方法，希望可以和大家分享(以表employee為例)。

SQL> desc employee

Name Null? Type

----------------------------------------- -------- ------------------

emp_id NUMBER(10)

emp_name VARCHAR2(20)

salary NUMBER(10,2)

可以通過下面的語句查詢重復(fù)的記錄：

SQL> select * from employee;

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

1 sunshine 10000

2 semon 20000

2 semon 20000

3 xyz 30000

2 semon 20000

SQL> select distinct * from employee;

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

2 semon 20000

3 xyz 30000

SQL> select * from employee group by emp_id,emp_name,salary having count (*)>1

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

2 semon 20000

SQL> select * from employee e1

where rowid in (select max(rowid) from employe e2

where e1.emp_id=e2.emp_id and

e1.emp_name=e2.emp_name and e1.salary=e2.salary);

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

3 xyz 30000

2 semon 20000

2. 刪除的幾種方法：

(1)通過建立臨時(shí)表來實(shí)現(xiàn)

SQL>create table temp_emp as (select distinct * from employee)

SQL> truncate table employee; (清空employee表的數(shù)據(jù))

SQL> insert into employee select * from temp_emp; (再將臨時(shí)表里的內(nèi)容插回來)

( 2)通過唯一rowid實(shí)現(xiàn)刪除重復(fù)記錄.在Oracle中，每一條記錄都有一個(gè)rowid，rowid在整個(gè)數(shù)據(jù)庫(kù)中是唯一的，rowid確定了每條記錄是在Oracle中的哪一個(gè)數(shù)據(jù)文件、塊、行上。在重復(fù)的記錄中，可能所有列的內(nèi)容都相同，但rowid不會(huì)相同，所以只要確定出重復(fù)記錄中那些具有最大或最小rowid的就可以了，其余全部刪除。

SQL>delete from employee e2 where rowid not in (

select max(e1.rowid) from employee e1 where

e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and e1.salary=e2.salary);--這里用min(rowid)也可以。

SQL>delete from employee e2 where rowid <(

select max(e1.rowid) from employee e1 where

e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and

e1.salary=e2.salary);

(3)也是通過rowid，但效率更高。

SQL>delete from employee where rowid not in (

select max(t1.rowid) from employee t1 group by

t1.emp_id,t1.emp_name,t1.salary);--這里用min(rowid)也可以。

EMP_ID EMP_NAME SALARY

1 sunshine 10000

3 xyz 30000

2 semon 20000

SQL> desc employee

Name Null? Type

----------------------------------------- -------- ------------------

emp_id NUMBER(10)

emp_name VARCHAR2(20)

salary NUMBER(10,2)

可以通過下面的語句查詢重復(fù)的記錄：

SQL> select * from employee;

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

1 sunshine 10000

2 semon 20000

2 semon 20000

3 xyz 30000

2 semon 20000

SQL> select distinct * from employee;

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

2 semon 20000

3 xyz 30000

SQL> select * from employee group by emp_id,emp_name,salary having count (*)>1

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

2 semon 20000

SQL> select * from employee e1

where rowid in (select max(rowid) from employe e2

where e1.emp_id=e2.emp_id and

e1.emp_name=e2.emp_name and e1.salary=e2.salary);

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

3 xyz 30000

2 semon 20000

2. 刪除的幾種方法：

(1)通過建立臨時(shí)表來實(shí)現(xiàn)

SQL>create table temp_emp as (select distinct * from employee)

SQL> truncate table employee; (清空employee表的數(shù)據(jù))

SQL> insert into employee select * from temp_emp; (再將臨時(shí)表里的內(nèi)容插回來)

( 2)通過唯一rowid實(shí)現(xiàn)刪除重復(fù)記錄.在Oracle中，每一條記錄都有一個(gè)rowid，rowid在整個(gè)數(shù)據(jù)庫(kù)中是唯一的，rowid確定了每條記錄是在Oracle中的哪一個(gè)數(shù)據(jù)文件、塊、行上。在重復(fù)的記錄中，可能所有列的內(nèi)容都相同，但rowid不會(huì)相同，所以只要確定出重復(fù)記錄中那些具有最大或最小rowid的就可以了，其余全部刪除。

SQL>delete from employee e2 where rowid not in (

select max(e1.rowid) from employee e1 where

e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and e1.salary=e2.salary);--這里用min(rowid)也可以。

SQL>delete from employee e2 where rowid <(

select max(e1.rowid) from employee e1 where

e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and

e1.salary=e2.salary);

(3)也是通過rowid，但效率更高。

SQL>delete from employee where rowid not in (

select max(t1.rowid) from employee t1 group by

t1.emp_id,t1.emp_name,t1.salary);--這里用min(rowid)也可以。

EMP_ID EMP_NAME SALARY

---------- ---------------------------------------- ----------

1 sunshine 10000

3 xyz 30000

2 semon 20000

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