Leetcode MySQL database topic 177

177. Nth Highest Salary

1、 Questions and answers

Table:Employee

+----+--------+
| Id | Salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+

Write a SQL query to get the nth highest salary from the Employee table.

To write SQL from Employee Get the number in the table n The highest salary

answer ：
delimiter $$ create function getNthHighestSalary(N int) returns int begin declare n1 int; set n1=N-1; return ( select distinct Salary from Employee order by Salary desc limit n1,1 ); end $$

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2、 Summary of knowledge points

• delimiter
• create function
• declare、set

１、 Why delimiter Because MySQL By default, a semicolon is used to end a command , When a command in the body of the function we define is written, it will end with a semicolon , and MySQL It will be mistaken that the function body has been defined , An error will be reported during operation . To do this, we need to define a new identifier to identify the end of a command .
２、
Create a new function ：

Create function function_name(parameter_type)
　　　　returns return_type
　　　　begin
　　　　#Function_content
　　　　end

Related instructions :
Function name ： Should be a legal identifier , And should not conflict with existing keywords . A function should belong to a database , have access to db_name.funciton_name Execute the database to which the current function belongs , Otherwise, it defaults to the current database .

parameter list ： You can have one or more function parameters , Even without parameters . For each parameter , It consists of parameter name and parameter type .
Return value ： Indicates the return value class type
The body of the function ： The function body of a custom function consists of several available MySQL sentence , Process control , Variable declaration and other statements . It should be noted that the function body must contain return Return statement .
3、
mysql Stored procedure , There are two ways to define variables ：

1. Use set or select Direct assignment , The variable name is @ start .
   for example :set @var=1;
   You can declare... Anywhere in a conversation , The scope is the entire session , Called session variable .
2. With declare Keyword declared variables , Can only be used in stored procedures , Called a stored procedure variable ,
   for example ：
   DECLARE var1 INT DEFAULT 0; Mainly used in the storage process , Or send parameters to storage .

Add

LeetCode Answers on ：

select IFNULL((select distinct(Salary) 
from Employee
order by Salary desc
limit 1,1),null) as SecondHighestSalary