What you do today can improve all your tomorrows.
Bear in mind: S = Single Responsibility Principle
O = Opened Closed Principle
L = Liskov Substitution Principle
I = Interface Segregation Principle
D = Dependency Inversion Principle
摘要：
select count(*) from project 返回表所有行总数select count(name) from project 返回表所有行中name不为null的行总数如果name确保不为null，上面两条查询语句的结果是一样的所以 select count(name) from project where name isnull是无效的 阅读全文
