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;
