PostgreSQL练习

建表

--department(dNo,dName,officeRoom,homepage)
--student(sNo,sName,sex,age,dNo)
--course(cNo,cName,cPNo,credit,dNo)
--sc(sNo,cNo,score,recordDate)CREATE TABLE department(dNo           CHAR(2)        NOT NULL UNIQUE,dName         VARCHAR(20),officeRoom    VARCHAR(40),homePage      VARCHAR(80),PRIMARY KEY(dNo)
);CREATE TABLE student(sNo      CHAR(6)        NOT NULL UNIQUE,sName        VARCHAR(20)    NOT NULL,sex     CHAR(2)        CHECK (sex IN('男','女')),      age        INT,dNo     CHAR(2),PRIMARY KEY(sNo),FOREIGN KEY (dNo) REFERENCES  department(dNo)
);CREATE TABLE course(cNo       CHAR(6)        NOT NULL UNIQUE,cName        VARCHAR(20)    NOT NULL,cPNo        CHAR(6),credit  INT,dNo           CHAR(2),PRIMARY KEY(cNo),FOREIGN KEY (cPNo) REFERENCES  course(cNo),FOREIGN KEY (dNo)  REFERENCES  department(dNo)
);CREATE TABLE sc(sNo       CHAR(6)        NOT NULL,cNo     CHAR(6)        NOT NULL,score       INT,recordDate    date           DEFAULT current_date,PRIMARY KEY(sNo,cNo),FOREIGN KEY (sNo) REFERENCES  student(sNo),FOREIGN KEY (cNo) REFERENCES  course(cNo)
);

插入数据

INSERT INTO department VALUES('01','信息学院','行政楼409','www.xxx.edu.cn');
INSERT INTO department VALUES('02','软件学院',null,null);
INSERT INTO department VALUES('03','理学院',null,null);
INSERT INTO department VALUES('04','文学院',null,null);
INSERT INTO department VALUES('05','外国语学院',null,null);INSERT INTO student VALUES('170101','宁灿',  '女',19,'01');
INSERT INTO student VALUES('170102','尹江月','女',19,'01');
INSERT INTO student VALUES('170103','杨佳伟','男',null,null);
INSERT INTO student VALUES('170104','杨何宇','男',19,'01');
INSERT INTO student VALUES('170105','胡耀斌','男',19,null);
INSERT INTO student VALUES('170106','李杨阳','女',20,'01');
INSERT INTO student VALUES('170107','杜利俊','女',18,'01');
INSERT INTO student VALUES('170108','钱多多','女',17,'01');
INSERT INTO student VALUES('170109','李佳伟','女',null,'01');
INSERT INTO student VALUES('170110','吴莫愁','女',21,'01');INSERT INTO student VALUES('170201','安相成','男',19,'02');
INSERT INTO student VALUES('170202','曹师好','男',null,'02');
INSERT INTO student VALUES('170203','雷霆',  '男',18,'02');
INSERT INTO student VALUES('170204','刘书敏','男',20,'02');
INSERT INTO student VALUES('170205','王兵',  '男',21,'02');
INSERT INTO student VALUES('170206','李佳成','男',19,null);
INSERT INTO student VALUES('170207','唐玉迎','女',17,'02');
INSERT INTO student VALUES('170208','杨曼婷','女',19,'02');INSERT INTO student VALUES('170301','张望',  '男',21,'03');
INSERT INTO student VALUES('170302','王芳',  '女',18,'03');
INSERT INTO student VALUES('170303','赵四海','男',19,'03');INSERT INTO student VALUES('170401','孙敏',  '女',null,null);
INSERT INTO student VALUES('170402','李忠国','男',null,'04');
INSERT INTO student VALUES('170403','钱紧',  '男',17,'04');
INSERT INTO student VALUES('170404','钱多多','女',20,'04');
INSERT INTO student VALUES('170405','管八方','男',21,'04');
INSERT INTO student VALUES('170406','王兵',  '男',19,'04');
INSERT INTO student VALUES('170407','张三丰','男',100,null);INSERT INTO course VALUES('030101','高等数学',null,2,'03');
INSERT INTO course VALUES('030102','线性代数',null,2,'03');
INSERT INTO course VALUES('030201','矩阵论','030102',3,'03');
INSERT INTO course VALUES('030202','概率论','030101',2,'03');
INSERT INTO course VALUES('030301','数理统计','030202',3,'03');INSERT INTO course VALUES('010101','信号与系统',null,2,'01');
INSERT INTO course VALUES('010102','数字电路','010101',2,'01');
INSERT INTO course VALUES('010103','数字信号处理','030301',3,'01');
INSERT INTO course VALUES('010201','模式识别','010103',3,'01');INSERT INTO course VALUES('020101','离散数学',null,2,'02');
INSERT INTO course VALUES('020102','程序设计基础',null,2,'02');
INSERT INTO course VALUES('020201','计算机组成原理','020101',3,'02');
INSERT INTO course VALUES('020202','面向对象程序设计','020102',2,'02');
INSERT INTO course VALUES('020203','编译原理','020101',2,'02');
INSERT INTO course VALUES('020301','数据结构','020202',3,'02');
INSERT INTO course VALUES('020302','操作系统','020201',3,'02');
INSERT INTO course VALUES('020401','数据库系统','020301',3,'02');
INSERT INTO course VALUES('020402','算法设计与分析','020301',3,'02');
INSERT INTO course VALUES('020403','形式语言与自动机','020203',3,'02');
INSERT INTO course VALUES('020501','移动计算','020102',2,'02');INSERT INTO course VALUES('040101','中国传统文化',null,1,'04');
INSERT INTO course VALUES('040102','近代世界史',null,1,'04');
INSERT INTO course VALUES('040103','现代文学',null,1,'04');
INSERT INTO course VALUES('040201','古典文学欣赏','040101',2,'04');
INSERT INTO course VALUES('040202','世界文学','040103',2,'04');
INSERT INTO course VALUES('040301','中国诗词欣赏','040201',2,'04');INSERT INTO sc VALUES ('170101','030101',91,to_date('2016-01-08','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','030102',83,to_date('2016-07-10','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','020101',88,to_date('2016-07-02','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','020102',92,to_date('2017-01-10','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','020201',70,to_date('2017-01-10','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','020202',80,to_date('2017-01-10','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170101','020203',null,null);
INSERT INTO sc VALUES ('170101','020301',null,null);
INSERT INTO sc VALUES ('170101','020302',null,null);
INSERT INTO sc VALUES ('170101','020401',null,null);
INSERT INTO sc VALUES ('170101','020402',null,null);INSERT INTO sc VALUES ('170102','030101',88,to_date('2016-01-08','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170102','030102',86,to_date('2016-07-10','yyyy-mm-dd'));
INSERT INTO sc VALUES ('170102','030201',58,null);
INSERT INTO sc VALUES ('170102','030202',90,null);
INSERT INTO sc VALUES ('170102','030301',70,null);
INSERT INTO sc VALUES ('170102','010101',85,null);
INSERT INTO sc VALUES ('170102','010102',68,null);
INSERT INTO sc VALUES ('170102','010103',80,null);
INSERT INTO sc VALUES ('170102','010201',78,null);INSERT INTO sc VALUES ('170103','030101',88,default);
INSERT INTO sc VALUES ('170103','030102',80,default);
INSERT INTO sc VALUES ('170103','030202',76,default);
INSERT INTO sc VALUES ('170103','010101',90,default);
INSERT INTO sc VALUES ('170103','010102',83,null);
INSERT INTO sc VALUES ('170103','010103',55,null);
INSERT INTO sc VALUES ('170103','010201',77,null);INSERT INTO sc VALUES ('170104','030101',null,null);INSERT INTO sc VALUES ('170105','030101',null,null);INSERT INTO sc VALUES ('170108','030101',90,null);
INSERT INTO sc VALUES ('170108','030102',87,null);
INSERT INTO sc VALUES ('170108','030202',78,null);
INSERT INTO sc VALUES ('170108','010101',57,null);
INSERT INTO sc VALUES ('170108','010102',56,null);
INSERT INTO sc VALUES ('170108','010103',54,null);
INSERT INTO sc VALUES ('170108','010201',50,null);INSERT INTO sc VALUES ('170110','030101',90,default);
INSERT INTO sc VALUES ('170110','030102',90,default);
INSERT INTO sc VALUES ('170110','010101',88,default);
INSERT INTO sc VALUES ('170110','010102',88,default);
INSERT INTO sc VALUES ('170110','010103',77,default);INSERT INTO sc VALUES ('170201','030101',88,null);
INSERT INTO sc VALUES ('170201','030102',83,null);
INSERT INTO sc VALUES ('170201','020101',79,null);
INSERT INTO sc VALUES ('170201','020102',84,null);
INSERT INTO sc VALUES ('170201','020201',75,null);
INSERT INTO sc VALUES ('170201','020202',80,null);
INSERT INTO sc VALUES ('170201','020301',82,null);
INSERT INTO sc VALUES ('170201','020302',53,null);
INSERT INTO sc VALUES ('170201','020401',78,null);
INSERT INTO sc VALUES ('170201','020402',58,null);INSERT INTO sc VALUES ('170202','030101',86,null);
INSERT INTO sc VALUES ('170202','030102',82,null);
INSERT INTO sc VALUES ('170202','020101',90,null);
INSERT INTO sc VALUES ('170202','020102',85,null);
INSERT INTO sc VALUES ('170202','020201',80,null);
INSERT INTO sc VALUES ('170202','020202',78,null);
INSERT INTO sc VALUES ('170202','020203',75,null);
INSERT INTO sc VALUES ('170202','020301',70,null);
INSERT INTO sc VALUES ('170202','020302',68,null);
INSERT INTO sc VALUES ('170202','020401',80,null);
INSERT INTO sc VALUES ('170202','020402',56,null);INSERT INTO sc VALUES ('170203','030101',null,null);
INSERT INTO sc VALUES ('170203','030102',null,null);INSERT INTO sc VALUES ('170205','030101',80,null);
INSERT INTO sc VALUES ('170205','030102',55,null);
INSERT INTO sc VALUES ('170205','020101',50,null);
INSERT INTO sc VALUES ('170205','020102',96,null);
INSERT INTO sc VALUES ('170205','020201',80,null);
INSERT INTO sc VALUES ('170205','020202',85,null);
INSERT INTO sc VALUES ('170205','020203',60,null);
INSERT INTO sc VALUES ('170205','020301',88,null);
INSERT INTO sc VALUES ('170205','020302',92,null);
INSERT INTO sc VALUES ('170205','020401',65,null);
INSERT INTO sc VALUES ('170205','020402',70,null);
INSERT INTO sc VALUES ('170205','020501',80,null);INSERT INTO sc VALUES ('170207','030101',null,null);
INSERT INTO sc VALUES ('170207','030102',null,null);INSERT INTO sc VALUES ('170208','030101',60,null);
INSERT INTO sc VALUES ('170208','030102',null,null);
INSERT INTO sc VALUES ('170208','020101',null,null);
INSERT INTO sc VALUES ('170208','020102',null,null);
INSERT INTO sc VALUES ('170208','020201',null,null);
INSERT INTO sc VALUES ('170208','020202',null,null);
INSERT INTO sc VALUES ('170208','020301',null,null);
INSERT INTO sc VALUES ('170208','020302',null,null);
INSERT INTO sc VALUES ('170208','020401',null,null);
INSERT INTO sc VALUES ('170208','020402',null,null);
INSERT INTO sc VALUES ('170208','020501',null,null);INSERT INTO sc VALUES ('170303','030101',90,null);
INSERT INTO sc VALUES ('170303','030102',88,null);
INSERT INTO sc VALUES ('170303','030201',92,null);
INSERT INTO sc VALUES ('170303','030202',93,null);
INSERT INTO sc VALUES ('170303','030301',94,null);INSERT INTO sc VALUES ('170401','040101',82,null);
INSERT INTO sc VALUES ('170401','040102',80,null);
INSERT INTO sc VALUES ('170401','040103',83,null);
INSERT INTO sc VALUES ('170401','040201',89,null);
INSERT INTO sc VALUES ('170401','040202',70,null);
INSERT INTO sc VALUES ('170401','040301',null,null);INSERT INTO sc VALUES ('170403','040201',95,null);
INSERT INTO sc VALUES ('170403','040202',88,null);
INSERT INTO sc VALUES ('170403','040301',80,null);INSERT INTO sc VALUES ('170404','040101',95,null);
INSERT INTO sc VALUES ('170404','040102',91,null);
INSERT INTO sc VALUES ('170404','040103',89,null);
INSERT INTO sc VALUES ('170404','040201',93,null);
INSERT INTO sc VALUES ('170404','040202',92,null);
INSERT INTO sc VALUES ('170404','040301',88,null);INSERT INTO sc VALUES ('170405','040102',70,null);
INSERT INTO sc VALUES ('170405','040201',58,null);
INSERT INTO sc VALUES ('170405','040202',66,null);
INSERT INTO sc VALUES ('170405','040301',77,null);INSERT INTO sc VALUES ('170406','040101',55,null);
INSERT INTO sc VALUES ('170406','040102',65,null);
INSERT INTO sc VALUES ('170406','040301',75,null);

练习1 单表查询

查询所有年龄大于等于20岁的学生学号、姓名；

select sno,sname
from student
where age >= 20;

查询所有姓钱的男生学号、姓名、出生年份；

select sno,sname,2020-age
from student
where sname like '钱%' and sex = '男';

LIKE操作符的模式匹配

查询所有学分大于3的课程名称；

select cname
from course
where credit > 3;

查询所有没有被分配到任何学院的学生姓名；

select sname
from student
where dno is null;

查询所有尚未设置主页的学院名称；

select dname
from department
where homepage is null;

练习2 聚集函数

查询各个学院的平均年龄；

select avg(age)
from student
group by dno;

查询每个学生选修课程的平均分；

select sno,avg(score)
from sc
group by sno
having avg(score) is not null
order by avg(score) desc;

order by 列名序；

查询各课程的平均分；

select cno,avg(score)
from sc
group by cno
having avg(score) is not null
order by avg(score) desc;

查询各学院开设的课程门数；

select dno,count(cno)
from course
where cno is not null
group by dno
order by count(cno) desc;

查询各门课程选修人数；

select cno,count(sno)
from sc
where cno is not null and sno is not null
group by cno
order by count(sno) desc;

练习3 多表查询

查询“信息学院”所有学生学号与姓名；

select sno,sname
from student
where dno in (select distinct dnofrom departmentwhere dname = '信息学院');

查询“软件学院”开设的所有课程号与课程名称；

select cno,cname
from course
where dno in (select dnofrom departmentwhere dname = '软件学院');

查询与“陈丽”在同一个系的所有学生学号与姓名；

select sno,sname
from student
where dno in (select dnofrom studentwhere sname = '陈丽');

查询与“张三”同岁的所有学生学号与姓名；

select sno,sname
from student
where age in (select agefrom studentwhere sname = '张三');

查询与“张三”同岁且不与“张三”在同一个系的学生学号与姓名；

select sno,sname
from student
where age in (select agefrom studentwhere sname = '张三')and dno not in (select dnofrom studentwhere sname = '张三');

查询学分大于“离散数学”的所有课程名称；

select cname
from course
where credit > (select creditfrom coursewhere cname = '离散数学');

查询选修了课程名为“组合数学”的学生人数；

select count(sno)
from sc
where cno = (select cnofrom coursewhere cname = '组合数学');

查询没有选修“离散数学”的学生姓名；

select sname
from student
where sno not in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '离散数学'));

查询与“算法设计与分析”、“移动计算”学分不同的所有课程名称；

select cname
from course
where credit not in (select creditfrom coursewhere cname = '算法设计与分析' or cname = '移动计算');

查询平均分大于等于90分的所有课程名称；

select cname
from course
where cno in (select cnofrom scgroup by cnohaving avg(score) >= 90);

查询选修了“离散数学”课程的所有学生姓名与成绩；

解法一：首先通过嵌套查询的方式找到表sno，sname和sno，score
然后将两个表连接成我们所需要的表

语句:select 表1/2.某，表1/2.某 … from (查询结果1) 表1 join (查询结果2) 表2 on (连接条件)

需要注意的是，自然连接是特殊的等值连接，等值连接只需指定两个属性相等，而自然连接是必须同名属性。本题中本来应该采取自然连接，但是postgreSQL不支持自然连接，所以这里其实是等值连接完成后在select里不选重复列。

select nametable.sno,sname,score
from (select sno,sname from student where sno in (select sno from sc where cno in (select cno from course where cname = '离散数学'))) nametable
join (select sno,score from sc where cno in (select cno from course where cname = '离散数学')) scoretable
on(nametable.sno = scoretable.sno);

解法二：多个表一起查询，查询完之后就是一个新表，注意把各个字段串联起来的条件

select student.sno,student.sname,sc.score
from student,sc
where student.sno = sc.snoandsc.cno in (select course.cnofrom coursewhere course.cname = '离散数学');

查询“王兵”所选修的所有课程名称及成绩；

select course.cname,sc.score
from course,sc
where course.cno = sc.cnoandsc.sno in (select student.snofrom studentwhere student.sname = '王兵');

查询所有具有不及格课程的学生姓名、课程名与成绩；

select student.sname,course.cname,sc.score
from student,course,sc
where student.sno = sc.snoandsc.score < 60andcourse.cno = sc.cno;

查询选修了“文学院”开设课程的所有学生姓名；

select student.sname
from student
where student.sno in (select snofrom scwhere cno in (select cnofrom coursewhere dno in (select dnofrom departmentwhere dname = '文学院')));

查询“信息学院”所有学生姓名及其所选的“信息学院”开设的课程名称；

select student.sname,course.cname
from student,course,sc
where student.dno in (select dno from department where dname = '信息学院')andsc.sno = student.snoand course.cno = sc.cnoandcourse.dno in (select dno from department where dname = '信息学院');

练习4 综合查询

查询所有学生及其选课信息（包括没有选课的学生）；

select t1.sno,t2.cno
from (select student.snofrom student) t1left join(select sc.sno,sc.cnofrom sc) t2on(t1.sno = t2.sno);

查询“形式语言与自动机”先修课的课程名称；

select t2.cname
from course t1,course t2
where t1.cname = '形式语言与自动机'andt2.cno = t1. cpno;

查询“形式语言与自动机”间接先修课课程名称；

select t3.cname
from course t1,course t2,course t3
where t1.cname = '形式语言与自动机'andt2.cno = t1.cpnoand t3.cno = t2.cpno;

查询先修课为编译原理的课程名称；

select t2.cname
from course t1,course t2
where t1.cname = '编译原理'andt2.cpno = t1.cno;

查询间接先修课为离散数学的课程名称；

select t3.cname
from course t1,course t2,course t3
where t1.cname = '离散数学'andt2.cpno = t1.cnoandt3.cpno = t2.cno;

查询所有没有先修课的课程名称；

select cname
from course
where cpno is null;

查询所有没选修“形式语言与自动机”课程的学生姓名；

select sname
from student
where sno not in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '形式语言与自动机'))

查询所有选修了“形式语言与自动机”但没选修其先修课的学生姓名；

select sname
from student
where sno in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '形式语言与自动机'))andsno not in (select sno from scwhere cno in (select cpnofrom coursewhere cno in (select cnofrom coursewhere cname = '形式语言与自动机')));

查询选修课程总学分大于等于28的学生姓名及其选修课程总学分；

select student.sname,sum(course.credit)
from student,course,sc
where student.sno = sc.snoandsc.cno = course.cno
group by student.sname
having sum(course.credit) >= 28;

查询选修了3门以上课程且成绩都大于85分的学生学号与姓名；

select student.sno,student.sname
from student
where student.sno in (select sc.snofrom scgroup by sc.snohaving count(sc.cno) > 3)       andstudent.sno not in (select sc.snofrom scwhere score <= 85);

查询恰好选修了3门课并且都及格的学生姓名；

select sname
from student
where sno in (select snofrom scwhere sno not in (select snofrom scwhere score < 60)group by snohaving count(cno) = 3);

查询人数多于6的学院名称及其学生人数；

select department.dname,count(student.sno)
from department,student
where department.dno = student.dno
group by department.dno
having count(student.sno) > 6;

查询平均成绩高于王兵的学生姓名；

select sname
from student
where sno in (select snofrom scgroup by snohaving avg(score) > all(select avg(score)from scgroup by snohaving sno in (select snofrom studentwhere sname = '王兵')));

查询所有选修了离散数学并且选修了编译原理课程的学生姓名；

select sname
from student
where student.sno in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '离散数学'))andstudent.sno in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '编译原理'));

查询软件学院离散数学课程平均分；

select avg(score)
from sc
where sno in (select snofrom studentwhere dno in (select dnofrom departmentwhere dname = '软件学院'))andsno in (select snofrom scwhere cno in (select cnofrom coursewhere cname = '离散数学'));

查询年龄与“软件学院”所有学生年龄都不相同学生姓名及其年龄和学院；

select student.sname,student.age,department.dname
from student,department
where student.age not in (select agefrom studentwhere dno in (select dnofrom departmentwhere dname = '软件学院'))anddepartment.dno = student.dno;

查询各学院选修同一门课人数大于4的学院、课程及选课人数；

select department.dname,course.cname,count(sc.sno)
from department,course,sc,student
where department.dno = student.dnoandsc.sno = student.snoandcourse.cno = sc.cno
group by department.dname,course.cname
having count(sc.sno) > 4;

group by不仅可以对一个字段进行聚合，还可以对多个字段的组合进行聚合

查询仅仅选修了“高等数学”一门课程的学生姓名；（学号、姓名及所在学院名称）

仅仅选修一门课的学生可以视为在选修了高等数学的学生集合并且不在选修高等数学以外的其他课程的学生集合

这里需要注意的是join的用法。join在inner join时可以不写，用字段相等的条件来代替，但是在出现left/right/full join 时就不能不用join了，此处有一个人的dno为null，如果再找dname的话就少了一行。

select t1.sno,t1.sname,t2.dname
from (select student.sno,student.sname,student.dnofrom studentwhere student.sno in (select snofrom scwhere sc.cno in (select cnofrom coursewhere course.cname = '高等数学'))andstudent.sno not in (select snofrom scwhere sc.cno in (select cnofrom coursewhere course.cname != '高等数学'))) t1left joindepartment t2on t1.dno = t2.dno;

上课时的总结：

查询结果和查询条件在同一个关系中——单表查询

查询结果在一个关系中，但查询条件用到了另一个关系——子查询，连接

查询结果不在同一个关系中——连接

查询平均学分积小于70分的学生姓名。

select student.sname
from student
where student.sno in (select snofrom (sc left join courseon sc.cno = course.cno) t1group by snohaving  (sum(t1.score*t1.credit)/sum(t1.credit)) < 70);

查询选修了“信息学院”开设全部课程的学生姓名。

https://blog.csdn.net/xmzhaoym/article/details/5249954

in 与 exists的区别，某字段 in (某字段集合)；exist (某查询结果集合是否为空)，exist 可以表示一个存在量词，一般也只是遇到全称量词或者全称量词蕴含式时才会用到

※关系除法可以用exist来完成（仅考虑特殊的全称量词）：

没有一门信息学院开设的课是他不选的——>不存在（信息学院开设的（不在他的选课单里面的））课

select student.sname
from student
where not exists (select *from department,coursewhere (department.dname = '信息学院'andcourse.dno = department.dno)andnot exists (select *from scwhere sc.sno = student.snoand                            course.cno = sc.cno));

查询选修了“杨佳伟”同学所选修的全部课程的学生姓名；

select t1.sname
from student t1
where not exists (select *from sc t2where (t2.sno in (select t3.snofrom student t3where t3.sname = '杨佳伟')andnot exists (select *from sc t4where t4.sno = t1.snoand                            t2.cno = t4.cno)));

练习5 DDL练习

创建2张表，信息如下：
- 图书（编号，书名，作者，ISBN，出版社编号，版本，出版日期）。主码为编号，ISBN唯一。出版社编号为外码，参照出版社表的编号。
- 出版社（编号，名称，地址，电话）。主码为编号。
- 要求：(1)创建表的同时创建约束；
  (2)删除所创建的表;
  (3)重新创建表，在表创建之后增加约束。

create table press(pno text primary key,pname text,address text,pn text);create table books(bno text primary key,bname text,aname text,isbn text unique,pno text references press(pno),ver text,pdate date);

drop table books;
drop table press;
--外键中发起引用的表先删，被引用的表后删

create table press(pno text,pname text,address text,pn text);create table books(bno text,bname text,aname text,isbn text,pno text,ver text,pdate date);
alter table press add primary key(pno);
alter table booksadd primary key(bno),add unique(isbn),add foreign key(pno) references press(pno);

(1)分别向两张表中各插入2行数据。
(2)将其中一个出版社地址变更一下。
(3)删除所插入数据。

insert into press values('某出版社1','某出版社','某地','20001023'),('某出版社2','某出版社','某地','20001023');
insert into books values('某编号1','某书','某人','某ISBN号1','某出版社1','某版本','2000-10-23'),('某编号2','某书','某人','某ISBN号2','某出版社1','某版本','2000-10-23');update press set address = '中国' where pno = '某出版社1';delete from books;
delete from press;

(1)创建一个软件学院所有选修了“离散数学”课程的学生视图，并通过视图插入一行数据。
(2)创建一个各门课程平均分视图。

对视图的更新可以唯一的转化为对于基本表的更新，那么更新是可以的

视图涉及聚集函数，那么更新一般是不被允许的

create view st as (select student.snamefrom student,department,sc,coursewhere student.dno in (select dnofrom departmentwhere department.dname = '软件学院')andsc.sno = student.snoandsc.cno in (select cnofrom coursewhere cname = '离散数学'))
with check option;insert into st values('刘铭帅');

这种更新即为非法的，为什么呢？因为我在这里给view加入了with check option的条件，这里view插入一个新的数据后，这个数据在表中的其他字段实际上是null，是不符合view的筛选条件的，所以不应该出现在view中。

运行结果：

这里按照题意就取消掉with check option了

create view avgs as (select course.cno,t1.avgg from course left join (select sc.cno,avg(sc.score) as avggfrom scgroup by sc.cno) t1oncourse.cno = t1.cno);

创建一张学生平均成绩表s_score(sNo,sName,avgscore),并通过子查询插入所有学生数据。

在数据库中，向数据库中插入数据，使用insert into关键字。在数据库中插入数据有三种方法。

1）插入单个字段的情况

insert into table_name(列名) values(值);

2）插入多个字段的情况

2.1）插入两个字段以上

insert into table_name(列名1，列名2，列名3,) values(值1,值2，值3);

2.2）插入全部所有字段

insert into table_name values(值1，值2，值3);//值要和表中的字段顺序类型一致

3）使用子查询向表中插入数据

insert into table_name 子查询select语句;//需要注意的是不能违反表table_name的约束条件，以及需要和table_name的字段一致，或者少于它，但是不能多于它。

create table s_score(sNo text unique not null,sName text,avgscore numeric(6,4));insert into s_score (select student.sno,student.sname,t1.avggfrom student left join (select sc.sno,avg(sc.score) as avggfrom scgroup by sc.sno) t1ont1.sno = student.sno);
select * from s_score;

练习6 DCL

尝试将多条SQL语句组成一个事务执行，体验提交和回滚操作。

一个事务transaction由begin…commit包含的语句构成，回滚可以使用rollback语句。