【题目】
选出所有 bonus < 1000 的员工的 name 及其 bonus。
Employee 表单
+-------+--------+-----------+--------+
| empId | name | supervisor| salary |
+-------+--------+-----------+--------+
| 1 | John | 3 | 1000 |
| 2 | Dan | 3 | 2000 |
| 3 | Brad | null | 4000 |
| 4 | Thomas | 3 | 4000 |
+-------+--------+-----------+--------+
empId 是这张表单的主关键字
Bonus 表单
+-------+-------+
| empId | bonus |
+-------+-------+
| 2 | 500 |
| 4 | 2000 |
+-------+-------+
empId 是这张表单的主关键字
输出示例:
+-------+-------+
| name | bonus |
+-------+-------+
| John | null |
| Dan | 500 |
| Brad | null |
+-------+-------+
来源:力扣(LeetCode)
链接:https://leetcode.cn/problems/employee-bonus
【思路】
左连接,判断条件加is null
SELECT name,bonus FROM Employee LEFT JOIN Bonus ON Bonus.empId = Employee.empId WHERE Bonus.bonus<1000 or Bonus.bonus IS NULL