Let me talk about the meaning of the mysql function:
A set of pre-compiled SQL statements, understood as batch statements
The purpose of using the function:
1. Improve code reusability
2. Simplify operation
3. Reduce the number of compilations and reduce the number of connections to the database server, which improves efficiency.
The difference between functions and stored procedures :
Stored procedure: There can be 0 return values or multiple return values, suitable for batch insertion and batch update
Function: There is one and only one return value , which is suitable for returning a result after processing the data.
One, create grammar:
create function 函数名（参数列表） return是返回类型
begin
函数体
end
#注意
1、参数列表包含两部分：参数名，参数类型
2、函数体：肯定会有return语句，如果没有会报错，如果return语句没有放在函数体的最后也不报错，但是不建议（没有意义）
3、函数体中仅有一句话，可以省略begin end
4、使用delimiter语句设置结束标记（demilter $）Two, call syntax
select function name (parameter list)
Example:
1. Return without participation
Returns the number of employees in the company
create function myf1（）returns int
begin
declare c int default 0;
select count(*) into c
from employees;
return c;
end $
select myf1()$Participate and return
#根据员工名返回工资
create function myf2 (empName varchar(20)) returns double
begin
set @sal=0#定义用户变量
select salary into @sal from employees where last_name=empName;
return @sal;
end $
select myf2('king') $Return the average salary of the department according to the department name
create function myf3(repName varchar(20)) returns double
begin
declare sal double;
select avg(salary) into sal
from employees e
join departments d on e.department_id=d.department_id
where d.department_name =repName;
return sal;
end $
select myf3('IT') $Three, view function
show create function function name;
Four, delete function
drop function function name