mysql FUNCTION

<!--创建函数-->

DROP FUNCTION IF EXISTS fn_classes_teacher_num;

CREATE FUNCTION fn_classes_teacher_num(id_in varchar(20))
RETURNS INTEGER
READS SQL DATA 
BEGIN
RETURN 
 (SELECT num_of_teacher from classes where id=id_in);

END;

<!--使用函数-->

select  fn_classes_teacher_num('1');