在SQL中删除重复记录的多种方法

 Name                                      Null?    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 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