用sql话语删除重复记录

用sql语句删除重复记录
Examples

For each department in the sample table oe.employees, the following example assigns numbers to each row in order of employee's hire date:

SELECT department_id, last_name, employee_id, ROW_NUMBER()   OVER (PARTITION BY department_id ORDER BY employee_id) AS emp_id   FROM employees;

DEPARTMENT_ID LAST_NAME                 EMPLOYEE_ID     EMP_ID
------------- ------------------------- ----------- ----------
           10 Whalen                            200          1
           20 Hartstein                         201          1
           20 Fay                               202          2
           30 Raphaely                          114          1
           30 Khoo                              115          2
           30 Baida                             116          3
           30 Tobias                            117          4
           30 Himuro                            118          5
           30 Colmenares                        119          6
           40 Mavris                            203          1
. . .
          100 Popp                              113          6
          110 Higgins                           205          1
          110 Gietz                             206          2

ROW_NUMBER is a nondeterministic function. However, employee_id is a unique key, so the results of this application of the function are deterministic.