注意点: ifnull函数的初衷是将为null的数据行转换为其他值 而不是把其他值转换成null
来源:Leetcode 链接:https://leetcode-cn.com/problems/second-highest-salary 【侵删】
ExampleA(第二高的薪水)
编写一个 SQL 查询,获取 Employee 表中第二高的薪水(Salary) 。
+----+--------+ | Id | Salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+
例如上述 Employee 表,SQL查询应该返回 200 作为第二高的薪水。如果不存在第二高的薪水,那么查询应返回 null。
+---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+
解题思路(dense_rank over limit 1,1 distinct)
# @1 select (select n.salary from (SELECT distinct salary, DENSE_RANK() OVER (ORDER BY salary DESC) rank_num FROM Employee limit 1,1) n ) as SecondHighestSalary; # @2 select ( select distinct salary from employee order by salary desc limit 1,1 ) as SecondHighestSalary