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1、假如数据库表中有int列,id列delete from MyTable where users_id not in ( select min(users_id)from MyTable group by users_password,users_name,users_phone )假如数据库表中没有int列,id列以表employee为例SQL desc employeeName Type- - - emp_id NUMBER(10)emp_name VARCHAR2(20) salary NUMBER(10,2) 可以通过下面的语句查询重复的记录:SQL select * from empl
2、oyee; 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 30000SQL select * from employee group by emp_id,emp_name,salary having coun
3、t (*)1 EMP_ID EMP_NAME SALARY - - - 1 sunshine 10000 2 semon 20000SQL 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 200002.
4、删除的几种方法:(1)通过建立临时表来实现 SQLcreate table temp_emp as (select distinct * from employee) SQL truncate table employee; (清空employee表的数据) SQL insert into employee select * from temp_emp; (再将临时表里的内容插回来)( 2)通过唯一rowid实现删除重复记录.在SQL中,每一条记录都有一个rowid,rowid在整个数据库中是唯一的,rowid确定了每条记录是在SQL中的哪一个数据文件、块、行上。在重复的记录中,可能所有列的内
5、容都相同,但rowid不会相同,所以只要确定出重复记录中那些具有最大或最小rowid的就可以了,其余全部删除。SQLdelete 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);-这里用min(rowid)也可以。SQLdelete from employee e2 where rowid delete from employee where rowid not in ( select max(t1.rowid) from employee t1 group by 1.emp_id,t1.emp_name,t1.salary); -这里用min(rowid)也可以。 EMP_ID EMP_NAME SALARY- - - 1 sunshine 10000 3 xyz 30000 2 semon 20000