[SQL]LeetCode176. 第二高的薪水 | Second Highest Salary
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Write a SQL query to get the second highest salary from the Employee table.
+----+--------+ | Id | Salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+
For example, given the above Employee table, the query should return 200 as the second highest salary. If there is no second highest salary, then the query should return null.
+---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+
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 | +---------------------+
方法1：使用子查询和LIMIT子句
算法：按降序对不同的工资进行排序，然后利用该LIMIT子句获得第二高的工资。
1 SELECT DISTINCT 2 Salary AS SecondHighestSalary 3 FROM 4 Employee 5 ORDER BY Salary DESC 6 LIMIT 1 OFFSET 1
但是，如果没有这样的第二高薪，这个解决方案将被判定为“错误答案”，因为此表中可能只有一条记录。为了解决这个问题，我们可以将其作为临时表。
1 SELECT 2 (SELECT DISTINCT 3 Salary 4 FROM 5 Employee 6 ORDER BY Salary DESC 7 LIMIT 1 OFFSET 1) AS SecondHighestSalary 8 ;
方法2：使用IFNULL和LIMIT子句
解决'NULL'问题的另一种方法是使用IFNULL如下功能。
1 SELECT 2 IFNULL( 3 (SELECT DISTINCT Salary 4 FROM Employee 5 ORDER BY Salary DESC 6 LIMIT 1 OFFSET 1), 7 NULL) AS SecondHighestSalary
105ms
1 # Write your MySQL query statement below 2 select ( 3 select distinct Salary from Employee order by Salary Desc limit 1 offset 1 4 )as SecondHighestSalary
106ms
1 # Write your MySQL query statement below 2 select max(salary) as SecondHighestSalary 3 from employee 4 where salary < (select max(salary) from employee)
108ms
1 # Write your MySQL query statement below 2 # select distinct Salary SecondHighestSalary from Employee order by Salary DESC limit 1,1 3 select ifNull((select distinct Salary from Employee order by Salary Desc limit 1,1),null) as SecondHighestSalary
110ms
1 # Write your MySQL query statement below 2 SELECT IFNULL( (SELECT DISTINCT salary 3 FROM Employee 4 ORDER BY salary DESC 5 LIMIT 1,1),NULL) AS SecondHighestSalary;
