SQL基础
包括：
- 数据查询：SELECT
- 数据定义语言：CREATE、ALTER和DROP
- 数据操纵语言：INSERT、UPDATE、DELETE
- 数据控制语言：GRANT、REVOKE
特点：
- 综合统一
- 高度非过程化
- 面向集合
- 既是独立的也是嵌入式语言
三级模式结构
- 外模式：视图、部分基本表
- 模式：基本表
- 内模式：存储文件
基本语句
建表
CREATE TABLE SC(
studentNo char(7) NOT NULL ,
courseNo char(3) NOT NULL ,
score numeric(5,1) DEFAULT 0 NOT NULL
CHECK(score BETWEEN 0.0 AND 100.0),
/*主码由两个属性构成，必须作为表级完整性约束进行定义*/
CONSTRAINT ScorePK PRIMARY KEY (studentNo, courseNo),
/*表级完整性约束条件，studentNo是外码，被参照表是Student*/
CONSTRAINT ScoreFK1 FOREIGN KEY (studentNo)
REFERENCES student(studentNo),
/*表级完整性约束条件，courseNo是外码，被参照表是Course*/
CONSTRAINT ScoreFK2 FOREIGN KEY(courseNo)
REFERENCES course(courseNo)
);
索引
CREATE INDEX ClassBirthIdx
ON Student(classNo, birthday DESC);
通配符
select Cno,Cname,credit from course where
Cname like 'DB\_%设__' escape '\';
排序
常用语句
检索全部学生都选修的课程号和课程名
SELECT CNO,CNAME FROM C WHERE CNO IN(SELECT DISTINCT CNO FROM SC GROUP BY CNO HAVING COUNT(SNO) = (SELECT COUNT (*) FROM S) );
检索至少选修Liu老师所教授课程中一门课程的女学生的姓名
SELECT DISTINCT S.SNAME FROM S,C,SC WHERE S.SNO=SC.SNO AND C.CNO=SC.CNO
AND S.SEX = '女' AND S.SNO IN (SELECT DISTINCT SNO FROM C,SC WHERE C.CNO=SC.CNO AND C.TEACHER = 'Liu');
求Liu老师所授课程的每门课程的平均成绩
SELECT CNAME, AVG(GRADE) FROM C,SC WHERE C.CNO=SC.CNO AND TEACHER='shu' GROUP BY CNAME;
统计每个学生选修课程的门数（超过2门的学生才统计）。要求输出学生学号和选修门数，查询结果按门数降序排列，若门数相同，按学号升序排列。
SELECT SNO,COUNT(CNO) FROM SC GROUP BY SNO
HAVING COUNT(CNO)>2 ORDER BY COUNT(CNO) DESC，SNO ASC;
查询每一门课的间接先修课
select A.Cno, A.Cname, B.Pre_Cno
from Course A,Course B
where A.Pre_Cno = B.Cno and B.Pre_Cno is not null;
查询成绩至少比选修了C02号课程的一个学生成绩低的学生学号
select Sno from SC where grade < any (
select Grade from SC where Cno = "C02"
) and Cno <> "C02";
查询成绩比所有选修了C02号课程的学生成绩低的学生学号
select Sno from SC where grade < all (
select Grade from SC where Cno = "C02"
) and Cno <> "C02"
查询选修了全部课程的学生姓名
SELECT SNAME
FROM Student
WHERE SNO IN (SELECT SNOFROM SCGROUP BY SNOHAVING COUNT(DISTINCT CNO) = (SELECT COUNT(*) FROM Course)
);或
select Sname from Student where not Exists (
select * from course where not Exists (
select * from SC where Sno=Student.Sno and Cno=Course.Cno)
);
查询所在系为自动化的学生以及姓李的学生的基本信息
select * from student where Sdept like '自动化'
Union
select * from student where Sname like '李%';
删除平均分在60分到70分之间的同学选课记录
DELETE FROM Score
WHERE studentNo IN (SELECT studentNo FROM Score GROUP BY studentNoHAVING avg(score) BETWEEN 60 AND 70 );
