Question

1我的目的是什么：

I try to get two person from each department with highest salary.

2我如何努力实现它：

DECLARE
  TYPE empl_table IS TABLE OF employees.employee_id%type INDEX BY binary_integer;
  empl empl_table;
  CURSOR departmennts_id IS 
    SELECT department_id FROM departments; 
BEGIN  

FOR depart_row IN departmennts_id  
loop
  SELECT employee_id BULK COLLECT into empl 
  FROM  
    (
      SELECT employee_id
      FROM employees
      where DEPARTMENT_ID= depart_row.department_id
      ORDER BY salary DESC
    )
WHERE ROWNUM<3;
END loop;
END;

3问题出在哪里：

where DEPARTMENT_ID= depart_row.department_id

当我将depart_row.department_id更改为固定身份证号码（例如80）查询工作。如果我使用depart_row.department_id，则empl.count为0。

我在哪里弄错了？

Answer 1

对于外部游标的每次迭代，您将行放入EMPL_TABLE。每次代码循环返回另一个department_id然后重新执行内部SELECT时， 将替换集合的内容 。因此，如果外部光标看到的LAST部门碰巧没有与之关联的员工，那么最终会得到一个空集合。

您最好的办法是取消DEPARTMENTS上的单独光标，只需使用一个可以完成所需操作的光标，如：

SELECT *
  FROM (SELECT DEPARTMENT_ID,
               SALARY,
               ROW_NUMBER() OVER
                 (PARTITION BY DEPARTMENT_ID
                  ORDER BY SALARY DESC) AS EMP_RANK
          FROM EMPLOYEES
          ORDER BY DEPARTMENT_ID, EMP_RANK)
  WHERE EMP_RANK < 3

SQLFiddle here

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在游标迭代循环中将游标变量传递给子查询

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