CREATE FUNCTION 函数名(参数列表) RETURNS 返回类型
BEGIN
函数体
return 值;
END

SELECT 函数名(参数列表)
执行完里面的语句并且显示返回值

#1.无参有返回
CREATE FUNCTION myf1() RETURNS INT 
BEGIN
            DECLARE c int DEFAULT 0;#定义变量
            SELECT count(*) INTO c#为变量赋值
            FROM employees;
            RETURN c;
END $

SELECT myf1()$


#2.有参有返回
#根据员工名，返回它的工资
CREATE FUNCTION myf2(empName VARCHAR(20)) RETURNS INT
BEGIN
            SET @sal=0; #定义用户变量：当前连接有效
            SELECT salary INTO @sal #赋值
            FROM employees
            WHERE last_name=empName;
            RETURN @sal;
END $

SELECT myf2(‘Hunold‘)$

#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 INT
BEGIN
            DECLARE sal DOUBLE;#加不加默认值都行
            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 myf2(‘IT‘)$

SHOW CREATE FUNCTION myf3;

DROP FUNCTION myf3;

CREATE FUNCTION myf2(empName VARCHAR(20)) RETURNS INT

#创建函数，实现传入两个float，返回二者之和
CREATE FUNCTION test_fun1(num1 FLOAT,num2 FLOAT) RETURNS FLOAT
BEGIN
            DECLARE sum FLOAT DEFAULT 0;
            SET sum=num1+num2;
            RETURN sum;
END$

SELECT test_fun1(1,2)$