如何查看员工在部门最晚生效日期是否为部门经理？

Question

我在 SQL Oracle 的视图中编码条件时遇到问题。

我有 2 个表格，这里是您需要的字段名称：

EMPLOYEE_TBL (employee_id)
DEPARTMENT_TBL (department_id, manager_id, effective_date, active_status)

我必须在 SELECT CASE 中编写以下条件：

FLAG = 'Y' if the employee is the manager of AT LEAST ONE department at the department's 
       latest (max) effective date and that the department has active_status = 'A' 
       at its max effective date
FLAG = 'N' otherwise

这是我目前所拥有的，但它并没有达到我想要的效果：

SELECT A.EMPLOYEE_ID, B.EFFECTIVE_DATE, B.ACTIVE_STATUS, 
 CASE WHEN EXISTS (SELECT DISTINCT Z.MANAGER_ID FROM DEPARTMENT_TBL Z 
                    WHERE Z.MANAGER_ID = B.MANAGER_ID
                      AND Z.DEPARTMENT_ID = B.DEPARTMENT_ID
                      AND Z.MANAGER_ID = A.EMPLOYEE_ID /* this is the condition */
                      AND Z.EFFECTIVE_DATE = (SELECT MAX(Y.EFFECTIVE_DATE) 
                                              FROM DEPARTMENT_TBL Y 
                                              WHERE Y.DEPARTMENT_ID = Z.DEPARTMENT_ID 
                                              AND Y.EFFECTIVE_DATE <= SYSDATE)
                      AND Z.ACTIVE_STATUS = 'A')
 THEN 'Y' ELSE 'N' END AS FLAG
FROM EMPLOYEE_TBL A LEFT JOIN DEPARTMENT_TBL B 
ON A.employee_id = B.manager_id

这里是 SQLFiddle：http://sqlfiddle.com/#!4/241d99/1

遗留问题：员工 35 的标志必须为“Y”，因为他是部门 D7777 在部门最大生效日期的经理。

这里是 DEPARTMENT_TBL：

DEPARTMENT_ID    MANAGER_ID    EFFECTIVE_DATE     EFFECTIVE_STATUS
 D1273            35            2006-01-01              A
 D1273            35            2011-12-21              A  -- here flag of 35 is 'N'
 D1273            04            2012-03-05              A
 D1000            04            2012-12-12              A
 D7777            04            2009-05-14              A 
 D7777            35            2011-09-26              A -- but here flag of 35 is 'Y'

如何解决这个问题？

Answer 1

您可以使用row_number() 获取部门的最新记录。这大大简化了查询：

select e.*,
       (case when d.department_id is not null then 'Y' else 'N' end) as isManager
from employee_tbl e left join
     (select d.*,
             row_number() over (partition by d.department_id
                                order by d.effective_date desc) as seqnum
      from department_tbl d
      where d.effective_date < sysdate
     ) d
     on e.department_id = d.department_id and d.active_status = 'A' and
        seqnum = 1;

Here's 修正了错字的 SQL Fiddle。