题目链接：点击打开链接
题目大意：略。
解题思路：略。
AC 代码
-- 解决方案(1) select employee_id,department_id from (select employee_id,department_id,row_number() over(partition by employee_id order by primary_flag desc) rno from employee) where rno=1 -- 解决方案(2) SELECT employee_id, department_id FROM Employee WHERE primary_flag = 'Y' UNION SELECT employee_id, department_id FROM Employee GROUP BY employee_id HAVING COUNT(*) = 1
