摘要：
from on join where group by with cube / with rollup having select distinct order by 阅读全文
摘要：
class Book: #类的成员变量 hello = "world" #类初始化转换器，类在外部初始化的时候 把title的值传给__title 类似的举例 def __init__(self,title,price): self.__title = title self.__price = pr 阅读全文