create table Student(
Sno char(7) not null primary key,Sname char(6) ,Ssex char(2) ,Sage int,Sdept char(10) )create table Course(Cno char(4) not null primary key,Cname char(20) ,Credit int ,Semester int )create table Sc(Sno char(7)not null,Cno char(4)not null,Grade int ,primary key(Sno,Cno),foreign key (Sno) references Student(Sno),foreign key (Cno) references Course(Cno))use SCS3–p47–查询全体学生的学号和姓名select Sno, Sname from Student --查询全体学生的姓名、学号和所在系select Sname, Sno, Sdept from Student --查询全部列select from Student–增加计算列 查询全体学生的姓名及出生年份 p48 例 select Sname ,2015-Sage from Student --增加常量列 例select Sname ,‘出生年份’, 2015-Sage from Studentselect Sname as 姓名 , ‘出生年份’ as 常量列, 2015-Sage as 年份 from Student–在选课表中查询那些学生选修了课程，列出选课学生的学号select Snofrom Sc-- distinct 去掉重复列 p49 学号不重复select distinct Sno from Sc–查询满足条件的元组p50–例查询计算机系全体学生的姓名select Snamefrom Studentwhere Sdept = ‘计算机系’ --例查询年纪在岁以下的学生的姓名和年纪select Sname, Sage from Studentwhere Sage <20–查询考试成绩不及格的学生的学号select distinct Sno from Sc where Grade <60–使用BETWEEN … AND 和NOT BETWEEN … AND 来确定范围 p50 --查询年纪在~30岁之间的学生姓名、所在系和年纪select Sname, Sdept,Sage from Student where Sage between 20 and 30-------------------------------------------------------------- select Sname,Sdept, Sage from Student where Sage >=20 and Sage <=30–查询年纪不在~30 之间的学生姓名、所在系和年纪select Sname,Sdept,Sage from Student where Sage not between 20 and 30---------------------------------------------------- select Sname,Sdept,Sage from Student where Sage <20 or Sage >30–确定集合使用IN运算符 p51–查询”信息系“、”数学系“、”计算机系“的学生的姓名和性别select Sname,Ssex from Student where Sdept in(‘信息系’, ‘数学系’, ‘计算机系’)----------------------------------------- select Sname, Ssex from Student where Sdept='信息系’or Sdept='数学系’or Sdept =‘计算机系’–查询既不是”信息系“、”数学系“，也不是”计算机系“的学生的姓名和性别select Sname, Ssex from Student where Sdept not in(‘信息系’, ‘数学系’, ‘计算机系’)-------------------------------------------------------------------select Sname, Ssex from Student where Sdept!=‘信息系’ and Sdept !='数学系’and Sdept !=‘计算机系’ --字符串匹配 LINK 运算符 p52–列名[NOT] LINK <匹配串>–例查询姓’张’的学生的详细信息 p52 select from Student where Sname like ‘张%’ --查询姓”张“或”李“或”刘“的学生的详细信息 select * from Studentwhere Sname like ‘[张李刘]%’---------------------------------------------------select * from Studentwhere Sname like ‘张%’ or Sname like ‘李%’ or Sname like ‘刘%’–查询名字中第二个字为”小“或”大“的学生的姓名和学号 select Sname, Snofrom Student where Sname like ‘[大小]%’ --查询所有不姓王也不姓张的学生姓名 select Snamefrom Studentwhere Sname not like ‘[王张]%’----------------------------------------------------------- select Sname from Studentwhere Sname like ‘[^王张]%’----------------------------------------------------------------- select Sname from Studentwhere Sname not like '王%'and Sname not like ‘张%’ --查询姓”王“且名字是个字的学生的姓名select Snamefrom Studentwhere Sname like ’ 王’ --查询姓”王“且名字是个字的学生的姓名 select Snamefrom Studentwhere Sname like ’ 王__’ --未去空格 --使用去掉尾随空格的函数：rtrim p54–使用格式：RTRIM （列名） select Snamefrom Studentwhere rtrim(Sname) like ‘王__’ --去空格–例查询没有考试成绩的学生的学号和课程号p54select Sno, Cno from Sc where Grade is null --查询所有考试成绩的学生的学号和课程号select Sno, Cnofrom Scwhere Grade is not null --多重查询where 字句中可以使用逻辑运算符AND 和OR 来组成多条查询 – 例查询计算机系年龄在岁以下的学生的姓名和年龄select Sname, Sagefrom Studentwhere Sdept = '计算机系’and Sage <20 --例子查询计算机系和信息系年龄大于等于岁的学生姓名、所在系和年龄select Sname, Sdept, Sagefrom Studentwhere (Sdept = ‘计算机系’ or Sdept = ‘信息系’)and Sage >=20–对查询结果进行排序p55–ORDER BY <列名> [ASC/DESC] 默认排列方式为升序排序ASC-- 例子将学生按年龄的升序排序select from Student order by (Sage) ASC --查询选修了“c002”号课程的学生的学号及其成绩，查询结果按成绩降序排列 select Sno, Gradefrom Scwhere Cno ='C002’order by (Grade)DESC–查询全体学生的信息，查询结果按所在系的系名升序排列，同一系学生按年龄降序排列select from Studentorder by Sdept,Sage ASC --使用聚合函数汇总数据–统计学生的总人数select COUNT() as学生人数from Student --统计选修课程的学生人数select COUNT(distinct Sno) --去掉重复学号from Sc–计算“”学生的选修门数和考试总成绩select COUNT() as 选修门数, SUM(Grade) as 总成绩from Scwhere Sno= ‘1512101’ --计算“c001”课程的考试平均成绩select AVG(Grade)from Scwhere Cno = ‘C001’ --查询“c001”课程的考试最高分和最低分select MAX(Grade) as 最高分 , MIN(Grade) as 最低分from Scwhere Cno = ‘c001’ --查询“”学生的选课门数、已考试课程门数以及考试最高分、最低分和平均分select COUNT()as 选课门数, COUNT(Grade)as 考试门数, MAX(Grade) as 最高分, MIN(Grade)as 最低分 , AVG(Grade)as 平均分from Scwhere Sno = ‘1512101’ --统计每门课程的选课人数，列出课程号和选课人数select Cno as 课程号, COUNT(Sno) as 选课人数from Sc group by(Cno)–统计每个学生的选课门数和平均成绩 p58select Sno as 学号,COUNT() as 选课门数,AVG(Grade) as 平均成绩from Scgroup by Sno–统计每个系学生的人数和平均成绩 p59select COUNT() as 学生人数, AVG(Sage)as 平均年龄from Studentgroup by Sdept–带where字句的分组。统计每个系的女生人数select Sdept ,COUNT() as 女生人数from Studentwhere Ssex = '女’group by Sdept --统计每个系男生人数和女生人数，以及男生的最大年龄和女生的最大年龄select Sdept,Ssex,COUNT() as 人数,MAX(Sage)from Studentgroup by Sdept, Ssex --使用having 语句–查询选修了门以上课程的学生的学号和选课门数select Sno ,COUNT() 选课门数from Sc group by Snohaving COUNT()>3–查询考试平均成绩超过的学生的学号、选课门数和平均成绩select Sno, COUNT()as 选课门数,AVG (Grade)as平均成绩from Scgroup by Sno having AVG(grade)>= 80–统计每个系的男生人数，只列出男生人数大于等于的系select Sdept,COUNT()as 男生人数from Student where Ssex = '男’group by Sdepthaving Count() >= 2–查询计算机系和信息管理系的学生的学生人数，语句有两种写法p61select Sdept,COUNT()from Studentgroup by Sdepthaving Sdept in(‘计算机系’,‘信息管理系’)--------------------------------------------------select Sdept , COUNT()from Student where Sdept in(‘计算机系’,‘信息管理系’)group by Sdept–多表连接查询–内连接–例查询每个学生及其选课的详细信息p62select * from Student join Sc on Student.Sno = Sc.Sno --将Student 与Sc 连接起来–去掉上述的重复列select Student.Sno, Sname,Ssex,Sage,Sdept,Cno,Gradefrom Student join Sc on Student.Sno = Sc.Sno;–例查询计算机系学生的修课情况，要求列出学生的学号、姓名、所选的课程号和成绩select Student.Sno, Sname, Cno, Gradefrom Student join Sc on Student.Sno = Sc.Sno --查询计算机系学生的修课情况，要求列出学生的学号、名字、所选课程号和成绩select Student.Sno ,Sname, Cno, Gradefrom Student join Sc on Sc.Sno = Sc.Sno where Sdept = ‘计算机系’–为表取别名p64–为表指定了别名时，所有用到表的地方都要使用别名select S.Sno ,Sname, Cno, Gradefrom Student S join Sc on S.Sno = Sc.Sno where Sdept = ‘计算机系’–查询"信息系"选修了"计算机文化学"课程的学生的成绩，要求列出学生的姓名、课程名和成绩–每连接一张表，就需要加一个join子句select Sname, Cname, Gradefrom Student S join Sc on S.Sno = Sc.Sno join Course C on C.Cno = Sc.Cnowhere Sdept = ‘计算机系’ and Cname = ‘计算机文化学’ --查询所有选修了Java课程的学生情况，列出学生姓名和所在系select Sname, Sdept from Student S join Sc on S.Sno = Sc.Sno join Course C on C.Cno = Sc.Cno where Cname = ‘Java’–例题用有分组的多表连接查询，统计每个系的学生的考试平均成绩p64select Sdept ,AVG(Grade) as 平均成绩from Student s join Sc on s.Sno = Sc.Snogroup by Sdept–有分组和行选择条件的多表连接查询–统计计算机系每门课程的选课人数、平均成绩、最高成绩和最低成绩select Cno, COUNT() as 选课人数,AVG(Grade) 平均成绩,MAX(Grade)as 最高成绩, MIN(Grade)as 最低成绩from Student s join Sc on s.Sno = Sc.Snowhere Sdept = '计算机系’group by Cno --自连接 相互连接的表在物理上为同一张表，但在逻辑上看成两张表–自连接一定要为表取别名p65-- 查询与刘晨在同一个系学习的学生的姓名和所在系select S2.Sname, S2.Sdeptfrom Student s1 join Student s2 on s1.Sdept = s2.Sdeptwhere s1.Sname = '刘晨’and s2.Sname !=‘刘晨’ --查询与"数据结构"学分相同的课程的课程名和学分select c2.Cname, c2.Creditfrom Course c1 join Course c2 on c1.Credit = c2.Creditwhere c1.Cname = ‘数据结构’ --外连接 p66 只限制一张表中的数据必须满足连接条件，而另一张表中的数据可以不满足连接条件–查询学生的选课情况，包括选了课程的学生和没有选课程的学生select Student.Sno ,Sname, Cno ,Gradefrom Student Left outer join Sc on Student.Sno = Sc.Sno --此查询也可以用右外连接实现select Student.Sno, Sname, Cno ,Gradefrom Sc right outer join Student on Student.Sno = Sc.Sno–查询哪些课程没有人选。列出其课程名select Cname from Course C left join Sc on C.Cno = Sc.Cno where Sc.Cno is null --或Sno is null–使用TOP 限制结果集p67–查询年级最大的三个学生的姓名、年龄及所在系select Top 3 Sname, Sage, Sdept from Studentorder by Sage DESC–若要包括年龄并列第三名所有的学生select TOP 3 with ties Sname, Sage, Sdept from Studentorder by Sage DESC–查询Java课程考试成绩前三名的学生的姓名、所在系和成绩select top 3 with ties Sname,Sdept,Gradefrom Student S join Sc on S.Sno = Sc.Sno join Course C on C.Cno = Sc.Cno where Sdept = 'Java’order by Grade DESC–子查询p68–查询与’刘晨’在同一个系学习的学生select Sno, Sname, Sdept from Studentwhere Sdept in ( select Sdept from Student where Sname = ‘刘晨’) --(包括刘晨) --表的链接来查询select S1.Sno, S1.Sname, S1.Sdept from Student S1 join Student S2 on S1.Sdept =S2.Sdeptwhere s2.Sname = ‘刘晨’ --第三种查询方法select s1.Sno,S1.Sname ,S1.Sdeptfrom Student s1,Student S2where S2.Sname = '刘晨’and s1.Sdept = S2.Sdept–不包括刘晨select Sno, Sname, Sdept from Studentwhere Sdept in ( select Sdept from Student where Sname = ‘刘晨’) and Sname !=‘刘晨’ --表的链接来查询select S1.Sno, S1.Sname, S1.Sdept from Student S1 join Student S2 on S1.Sdept =S2.Sdeptwhere s2.Sname = ‘刘晨’ and s2.Sname != ‘刘晨’ --第三种查询方法select s1.Sno,S1.Sname ,S1.Sdeptfrom Student s1,Student S2where S2.Sname = '刘晨’and s2.Sname != ‘刘晨’ and s1.Sdept = S2.Sdept–查询考试成绩大于分的学生的学号和姓名–子查询select Sno,Snamefrom Student where Sno in( select Sno from Sc where Grade > 90) --表的连接select S.Sno ,Sname from Student S join Sc on S.Sno = Sc.Sno where Grade > 90–第三种查询方法select Student.Sno,Snamefrom Student,Scwhere Student.Sno = Sc.Sno and Grade > 90 --子查询的多表连接–查询选修了Java课程的学生的学号和姓名p70select Sno, Sname from Student where Sno in ( select Sno from Sc where Cno in ( select Cno from Course where Cname =‘Java’))–多表连接来查询select Sc.Sno, Snamefrom Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cnowhere Cname =‘Java’–例统计选修了Java 课程的学生的选课门数和平均成绩select Sno 学号,COUNT () as 选课门数, AVG(Grade)as 平均成绩from Sc where Sno in ( select Sno from Sc join Course on Sc.Cno = Course.Cno where Cname =‘Java’)group by Sno–嵌套的子查询 select Sno 学号,COUNT () as 选课门数, AVG(Grade)as 平均成绩from Scwhere Sno in ( select Sno from Sc where Cno in ( select Cno from Course where Cname = ‘Java’))group by Sno–嵌套子查询–使用子查询进行比较测试p71–where 表达式比较运算符(子查询)–例查询选了"c005"课程且成绩高于此课程的平均成绩的学生的学号和成绩–1、计算c005号课程的平均成绩select AVG(Grade)from Sc where Cno = ‘c005’ --结果为–2、查询c005号课程所有的考试成绩中，高于分的学生的学号和成绩select Sno,Gradefrom Scwhere Cno = ‘c005’ and Grade > 73–将上述两个查询语句合起来select Sno,Gradefrom Scwhere Cno = ‘c005’ and Grade > ( select AVG(Grade) from Sc where Cno = ‘c005’ )–例查询计算机系年龄最大的学生的姓名和年龄select Sname, Sage from Studentwhere Sdept = ‘计算机系’ and Sage = ( select MAX(Sage) from Student where Sdept = ‘计算机系’)–例查询Java考试成绩高于Java平均成绩的学生的姓名、所有系和Java成绩p72select Sname, Sdept, Gradefrom Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cnowhere Cname = ‘Java’ and Grade > ( select AVG(Grade) from Sc join Course on Sc.Cno = Course.Cno where Cname = ‘Java’ )–使用子查询进行存在性测试–where [NOT] exists(子查询)–查询选修了"c001"号课程的学生姓名–带有exists谓词的查询是先执行外层查询，然后再执行内层查询select Snamefrom Student where exists ( select from Sc where Sno = Student.Sno and Cno = ‘c001’)–上述的查询等价于以下语句select Sname from Student join Sc on Sc.Sno = Student.Sno where Cno = ‘c001’-- 或select Sname from Student where Sno in ( select Sno from Sc where Cno = ‘c001’) --查询没选c001号课程的学生的姓名和所在系p73–普通查询(错误的)select distinct Sname, Sdeptfrom Student,Scwhere Student.Sno = Sc.Sno and Cno !=‘c001’–多表连接实现(错误的)select distinct Sname,Sdeptfrom Student join Sc on Student.Sno = Sc.Snowhere Cno !=‘c001’–用嵌套子查询实现–1、在子查询中否定 (错误的)select Sname,Sdeptfrom Studentwhere Sno in ( select Sno from Sc where Cno !=‘c001’) --2、在外层查询中否定p74 问题：结果和其他的不一样具体原因如p75select Sname,Sdeptfrom Studentwhere Sno NOT IN (select Sno from Sc where Cno =‘c001’)–用相关子查询实现–1、在子查询中否定 (错误的)select Sname, Sdeptfrom Studentwhere exists ( select * from Sc where Sno = Student.Sno and Cno !=‘c001’) --2、在外层查询中否定 问题：结果和其他的不一样 具体原因如p75select Sname, Sdeptfrom Studentwhere not exists ( select * from Sc where Sno = Student.Sno and Cno =‘c001’)–注意：否定放置在外层查询中时，其结果是正确的–例查询计算机系没有选修Java课程的学生的姓名和性别select distinct Sname,Ssex,Sdept from Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cnowhere Sdept = '计算机系’and Cname !=‘Java’----------------------------------------------select distinct Sname, Ssex,Sdept from Student,Sc,Coursewhere Student.Sno = Sc.Sno and Sc.Cno = Course.Cno and Sdept = '计算机系’and Cname !=‘Java’---------------------------------------------- select Sname,Ssex,Sdeptfrom Studentwhere Sno in ( select Sno from Sc where Cno in( select Cno from Course where Cname !=‘Java’))and Sdept = ‘计算机系’------------------------------------------------select Sname,Ssex,Sdeptfrom Studentwhere Sno in ( select Sno from Sc join Course on Sc.Cno = Course.Cno where Cname!= ‘Java’)and Sdept = ‘计算机系’-----------------------------------------------------以上几种结果是错误的 否定放置在外层查询中时，其结果是正确的select Sname, Ssex,Sdept p75from Studentwhere Sno not in ( select Sno from Sc join Course on Sc.Cno = Course.Cno where Cname = ‘Java’)and Sdept = ‘计算机系’–4.2 数据更改p75–4.2 数据更改p75–插入数据 INSERT 语句的格式–INSERT [INTO] <表名> [(<列名表> [,…, … , n])] VALUES (值列表)–例将新生记录(1521104，陈东，男，岁，信息系) 插入Student表中 p75insert into Student values(‘1521104’, ‘陈东’,‘男’,18,‘信息系’)select * from Student–给Sc表中的成绩设置默认值为nullalter table Sc add default null for Grade–例子在Sc表中插入一条新记录，学号为"1521104"，选的课程号为"c001",成绩暂缺–因为提供的值的个数与表中的列的个数不一致，因此在插入语句中必须列出列名 insert Sc(Sno ,Cno ) values (‘1521104’,‘c001’) --相当于 insert Sc values (‘1521104’,‘c001’,null) select * from Sc–更新数据 p76–Update <表名> set <列名> = 表达式[,…,…n]-- [where 更新条件]–例将所有学生的年龄加update Student set Sage = Sage +1–将"1512101"学生的年龄改为岁update Student set Sage = 21 where Sno = ‘1521101’ --将计算机系全体学生成绩加分–子查询语句实现update Sc set Grade = Grade+5 where Sno in ( select Sno from Student where Sdept = ‘计算机系’ ) -------------------------------------------------------------------用多表连接实现语句update Sc set Grade = Grade+5from Student join Sc on Student.Sno = Sc.Sno where Sdept = ‘计算机系’–4.2.3删除数据 p77–DELETE 语句的格式：DELETE [from] <表名> {WHERE删除条件}–无条件删除 例删除所有学生的选课记录delete from Sc–有条件的删除–删除所有不及格学生的选课记录 delete from Sc where Grade < 60–例子删除计算机系不及格学生的选课情况–用子查询实现delete from Sc where Grade < 60 and Sno in ( select Sno from Student where Sdept = ‘计算机系’–用多表连接来实现语句delete from Sc from Sc join Student on Sc.Sno = Student.Sno where Sdept = '计算机系’and Grade < 60 --4.3数据查询扩展 --将查询结果保存到新表中 p77-p78 --使用select查询数据时，要将结果保存到一个表中，可以通过select语句和into子句实现 --select 查询列表序列into <新表名> —from 数据源 – … 其他行选择、分组等语句 --例查询计算机系学生的姓名、选修的课程名和成绩，并将查询结果保存到永久表S_C_G中语句 p78 select Sname, Cname, Grade into S_C_G from Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cno where Sdept = ‘计算机系’ – 例子统计每个系的学生人数，并将结果保存到永久表dept_cnt中 – b必须为COUNT() 列取别名，否则无法创建新表 select Sdept, COUNT() as 学生人数 into dept_cnt from Student group by Sdept --CASE表达式 p78–例查询选了Java课程的学生的学号、姓名、所在系和成绩，并对所在系进行如下处理：–当所在系为计算机系时，在查询结果中显示CS；当所在系为信息系时，在查询结果中显示IM–当所在系为数学系时，在查询结果中显示MAselect Sc.Sno 学号,Sname 姓名, CASE Sdept when ‘计算机系’ then ‘CS’ when ‘信息系’ then ‘IM’ when '数学系’then ‘MA’ END as 所在系, Grade 成绩from Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cnowhere Cname = ‘Java’–搜索CASE表达式p79-80–比如成绩在-90之间，则简单CASE表达式实现不了，这是就要使用搜索CASE表达式–用搜索CASE表达式的语句为select Sc.Sno 学号,Sname 姓名, CASE when Sdept = ‘计算机系’ then ‘CS’ when Sdept = ‘信息系’ then ‘IM’ when Sdept = '数学系’then ‘MA’ END as 所在系,Grade 成绩from Student join Sc on Student.Sno = Sc.Sno join Course on Course.Cno = Sc.Cnowhere Cname = ‘Java’–例查询"c001"课程的考试情况，列出学号、成绩以及成绩等级，对成绩等级的处理如下：p80–成绩大于等于为优，成绩-89之间为良，成绩-79之间为中，成绩在-69之间为及格，成绩小于为不及格select Sc.Sno 学号, Grade 成绩, CASE when Grade >=90 then ‘优’ when Grade between 80 and 89 then ‘良’ when Grade between 70 and 79 then ‘中’ when Grade between 60 and 69 then ‘及格’ when Grade < 60 then ‘不及格’ END as 成绩等级from Scwhere Cno = ‘c001’
