--创建数据库(文件：主要数据文件mdf==1，次要数据文件ndf>=0，日志文件ldf>=1)

--文件组：当1mdf,5个ndf(1,2,2),10个ldf(３，３，４),将它们分成多个组存放

CREATE database studb;

--创建表teacher,student

create table teacher

(

tid int(10) primary key auto_increment,

tname varchar(20),

tage int(10)

);

use studb;

create table student

(

sid int(10) primary key auto_increment,

sname varchar(20),

sage int(10),

tid int(10) REFERENCES teacher(tid)

);

--外键约束：你问张三的老师是谁？？

--select teacher.tname from teacher,student where student.sname = '张三'

select t.tname from teacher t,student s where s.sname = '张三' and t.tid = s.tid

--创建课程表

create table course

(

cid int(10) primary key,

cname varchar(20),

tid int(10) REFERENCES teacher(tid)

);

--创建分数表

create table sc

(

scid int(10) primary key,

sid int(10) REFERENCES student(sid),

cid int(10) REFERENCES course(cid),

score int(10)

);

--联合查询：等值查询

--1..

select c.cname from course c,student s,sc where s.sname = '小张'

and s.sid = sc.sid and c.cid = sc.cid;

--2..

select sname from student s,course c,sc where c.cname='android' and sc.score>=60

and s.sid = sc.sid and c.cid = sc.cid;

--3..

--子查询：当条件也要查询的时候,我只知道学号，我不知道"小张"这个字段,那你知道小张的学号　吗

delete from sc where sid = (select sid from student where sname = '小张');

--子查询中间的符号一定是父查询与子查询两张表关联的字段(一般是主外键)

--4..

update sc set score=score+5 where cid=????;

select tid from teacher where tname='李老师' ==1

select cname from course where tid = 1 ==课程名字，李老师教的

select cid from course where cname='android' ==课程ID

update sc set score=score+5 where cid=

(

select cid from course where cname=

(

select cname from course where tid =

(

select tid from teacher where tname='李老师'

)

)

);