2021-06-30

create database one20210605 default charset=utf8;

use one20210605;

create table student(

sid int , # 学生的id

`name`varchar(10), # 学生姓名

saddress varchar(100) # 学生地址

);

create table course (

cid int , # 课程id

sid int , # 选课的学生id

cname varchar(100) # 课程的名字

);

insert into student values (1 ,"关羽","许昌"),(2,"孔明","南阳"),(3,"张飞","河北"),(4,"刘备","四川"),(5,"阿斗","蜀国");

insert into course values ( 101 , 1 ,"三百回合不累法"),(102,2,"劝人投降话术"),(101,3,"三百回合不累法"),(102,4,"劝人投降话术"),(103,6,"如何俘获大乔和小乔");

select * from student;

select * from course;

-- 交叉查询 (笛卡尔积查询)

select * from student , course;

select * from student , course where student.sid = course.sid;

-- 内连接

select * from student inner join course on student.sid=course.sid;

-- 左外连接

select * from student left join course on student.sid = course.sid;