--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
sql;">
create table teacher
(
tid int(10) primary key auto_increment,tname varchar(20),tage int(10)
);
use studb;
sql;">
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？？
sql;">
--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
sql;">
create table course
(
cid int(10) primary key,cname varchar(20),tid int(10) REFERENCES teacher(tid)
);
--创建分数表
sql;">
create table sc
(
scid int(10) primary key,sid int(10) REFERENCES student(sid),cid int(10) REFERENCES course(cid),score int(10)
);
sql;">
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..
=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
sql;">
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..
sql;">
update sc set score=score+5 where cid=????;
原文链接：https://www.f2er.com/mssql/62910.htmlselect 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'
)
)
);
