Leetcode Mysql 1789. 员工的直属部门（DAY 12）

原题题目

代码实现（首刷自解）

# Write your MySQL query statement below
SELECT employee_id,department_id
FROM employee AS e
GROUP BY employee_id
HAVING COUNT(*) = 1UNION
SELECT employee_id,department_id
FROM employee AS e
WHERE primary_flag = 'Y'