常用SQL語句查詢分享_MsSql

--建立資料庫(檔案：主要資料檔案mdf==1，次要資料檔案ndf>=0，記錄檔ldf>=1)
--檔案組：當1mdf,5個ndf(1,2,2),10個ldf(3,3,4),將它們分成多個組存放

CREATE database studb;

--建立表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) );

--外鍵約束：你問張三的老師是誰？？

--select teacher.tname from teacher,student where student.sname = '張三'select t.tname from teacher t,student s where s.sname = '張三' and t.tid = s.tid

--建立課程表

create table course(cid int(10) primary key,cname varchar(20),tid int(10) REFERENCES teacher(tid));

--建立分數表

create table sc(scid int(10) primary key,sid int(10) REFERENCES student(sid),cid int(10) REFERENCES course(cid),score int(10));

--聯集查詢：等值查詢
--1..

select c.cname from course c,student s,sc where s.sname = '小張' 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>=60and s.sid = sc.sid and c.cid = sc.cid;

--3..
--子查詢：當條件也要查詢的時候,我只知道學號，我不知道"小張"這個欄位,那你知道小張的學號　嗎

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

--子查詢中間的符號一定是父查詢與子查詢兩張表關聯的欄位(一般是主外鍵)

--4..

update sc set score=score+5 where cid=????;select tid from teacher where tname='李老師' ==1select cname from course where tid = 1 ==課程名字，李老師教的select cid from course where cname='android' ==課程IDupdate 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='李老師')));