函数案例2：有参有返回

案例1：根据员工名 ，返回他工资

create function myf2(empName varchar(20)) returns  double
begin 
    set @sql=0;#定义用户变量
    select salary
    from employees
    where last_name = empName；
    return @sql；
end $;
select myf2('k_ing') $

案例2： 根据部门名，返回该部门的平均工资

create function myf3(deptName 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 =  deptName;
    return sal;
end $


select myf3('技术部');