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(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;
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。
如果該表需要刪除重復(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select即得到了Name，Address不重復(fù)的結(jié)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有一段時間了，發(fā)現(xiàn)在我建了一個用來測試的表(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實現(xiàn)刪除重復(fù)記錄;還可以建臨時表來實現(xiàn)...這個只提到其中的幾種簡單實用的方法，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)通過建立臨時表來實現(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; (再將臨時表里的內(nèi)容插回來)
( 2)通過唯一rowid實現(xiàn)刪除重復(fù)記錄.在Oracle中，每一條記錄都有一個rowid，rowid在整個數(shù)據(jù)庫中是唯一的，rowid確定了每條記錄是在Oracle中的哪一個數(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)通過建立臨時表來實現(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; (再將臨時表里的內(nèi)容插回來)
( 2)通過唯一rowid實現(xiàn)刪除重復(fù)記錄.在Oracle中，每一條記錄都有一個rowid，rowid在整個數(shù)據(jù)庫中是唯一的，rowid確定了每條記錄是在Oracle中的哪一個數(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