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数据库查询——第几高的数据?
2022-07-07 21:54:00 【流楚丶格念】
数据表
Employee 表:
+-------------+------+
| Column Name | Type |
+-------------+------+
| id | int |
| salary | int |
+-------------+------+
id 是这个表的主键。
表的每一行包含员工的工资信息。
题目2:第二高的薪水
编写一个 SQL 查询,获取并返回 Employee 表中第二高的薪水 。如果不存在第二高的薪水,查询应该返回 null 。
查询结果如下例所示。
示例 1:
输入:
Employee 表:
+----+--------+
| id | salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
输出:
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200 |
+---------------------+
示例 2:
输入:
Employee 表:
+----+--------+
| id | salary |
+----+--------+
| 1 | 100 |
+----+--------+
输出:
+---------------------+
| SecondHighestSalary |
+---------------------+
| null |
+---------------------+
解答
select ifNull(
(select distinct salary
from Employee
order by Salary Desc
limit 1,1),null
) as SecondHighestSalary;
题目3:第N高的薪水
编写一个SQL查询来报告 Employee 表中第 n 高的工资。如果没有第 n 个最高工资,查询应该报告为 null 。
查询结果格式如下所示。
示例 1:
输入:
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
n = 2
输出:
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200 |
+------------------------+
示例 2:
输入:
Employee 表:
+----+--------+
| id | salary |
+----+--------+
| 1 | 100 |
+----+--------+
n = 2
输出:
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| null |
+------------------------+
解答
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
declare m int;
SET m = N-1;
RETURN (
# Write your MySQL query statement below.
select ifNull(
(
select distinct salary
from Employee
order by salary desc
limit 1 offset m
),null)
);
END
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