1.集合查询
集合操作的种类
并操作UNION
交操作INTERSECT
差操作EXCEPT
参加集合操作的各查询结果的列数必须相同;对应项的数据类型也必须相同
查询计算机科学系的学生及年龄不大于19岁的学生。
SELECT *
FROM Student
WHERE Sdept= 'CS'
UNION
SELECT *
FROM Student
WHERE Sage<=19;
UNION：将多个查询结果合并起来时，系统自动去掉重复元组
UNION ALL：将多个查询结果合并起来时，保留重复元组
查询选修了课程1或者选修了课程2的学生。
SELECT Sno
FROM SC
WHERE Cno=' 1 '
UNION
SELECT Sno
FROM SC
WHERE Cno= ' 2 ';
查询计算机科学系的学生与年龄不大于19岁的学生的交集。
SELECT *
FROM Student
WHERE Sdept='CS'
INTERSECT
SELECT *
FROM Student
WHERE Sage<=19
实际上就是查询计算机科学系中年龄不大于19岁的学生。
SELECT *
FROM Student
WHERE Sdept= 'CS' AND Sage<=19;
查询既选修了课程1又选修了课程2的学生。
SELECT Sno
FROM SC
WHERE Cno=' 1 '
INTERSECT
SELECT Sno
FROM SC
WHERE Cno='2 ';
也可以表示为：
SELECT Sno
FROM SC
WHERE Cno=' 1 ' AND Sno IN
(SELECT Sno
FROM SC
WHERE Cno=' 2 ');
查询计算机科学系的学生与年龄不大于19岁的学生的差集。
SELECT *
FROM Student
WHERE Sdept='CS'
EXCEPT
SELECT *
FROM Student
WHERE Sage <=19;
实际上是查询计算机科学系中年龄大于19岁的学生
SELECT *
FROM Student
WHERE Sdept= 'CS' AND Sage>19;
2.于派生表的查询
子查询不仅可以出现在WHERE子句中，还可以出现在FROM子句中。
这时子查询生成的临时派生表（Derived Table）成为主查询的查询对象
找出每个学生超过他自己选修课程平均成绩的课程号
SELECT Sno, Cno
FROM SC, (SELECTSno, Avg(Grade)
FROM SC
GROUP BY Sno)
AS Avg_sc(avg_sno,avg_grade)
WHERE SC.Sno = Avg_sc.avg_sno
and SC.Grade >=Avg_sc.avg_grade
如果子查询中没有聚集函数，派生表可以不指定属性列，子查询SELECT子句后面的列名为其缺省属性。
查询所有选修了1号课程的学生姓名，可以用如下查询完成：
SELECT Sname
FROM Student,
(SELECT Sno FROM SC
WHERE Cno=' 1 ') AS SC1
WHERE Student.Sno=SC1.Sno;
3.Select语句的一般形式
SELECT [ALL|DISTINCT]
<目标列表达式> [别名] [ ,<目标列表达式> [别名]] ...
FROM <表名或视图名> [别名]
[ ,<表名或视图名> [别名]] ...
|(<SELECT语句>)[AS]<别名>
[WHERE <条件表达式>]
[GROUP BY <列名1>[HAVING<条件表达式>]]
[ORDER BY <列名2> [ASC|DESC]];
1. 目标列表达式的可选格式
目标列表达式格式
（1） *
（2） <表名>.*
（3） COUNT([DISTINCT|ALL]* )
（4） [<表名>.]<属性列名表达式>[,<表名>.]<属性列名表达式>]...
其中<属性列名表达式>可以是由属性列、作用于属性列 的聚集函数和常量的任意算术运算（+，-，*，/）组成的 运算公式
2. 聚集函数的一般格式
3. WHERE子句的条件表达式的可选格式
4.练习
/*（1）查询选修了81003号课程的学生姓名；*/
/*方法1：连接查询*/
select sname
from Student,SC
where Student.Sno=SC.Sno and SC.Cno='81003';
/*方法2：嵌套in*/
select sname
from Student
where Sno in (select Sno
from SC
where Cno='81003');
/*方法3：嵌套exists*/
select sname
from Student
where exists (select *
from SC
where Sno=Student.Sno and Cno='81003');
/*（2）查询选修了学分为3的课程的学生学号和姓名；*/
/*方法1：连接查询*/
select Student.Sno ,student.sname
from Student,SC,Course
where Student.Sno=SC.Sno and SC.Cno=Course.Cno and Ccredit='3';
/*方法2：嵌套in*/
select Sno ,sname
from Student
where Sno in (select Sno
from SC
where Cno in (select Cno
from Course
where Ccredit='3'));
/*（3）找出每个超过其所在专业平均年龄的学号，姓名和年龄*/
/*方法1：嵌套相关查询*/
select sno,sname,YEAR(GETDATE())-YEAR(sbirthdate)as'年龄'
from Student
where YEAR(GETDATE())-YEAR(sbirthdate)> any(select AVG(YEAR(GETDATE())-YEAR(sbirthdate))
from Student
group by Smajor);
/*方法2：派生表*/
select distinct sno,sname,YEAR(GETDATE())-YEAR(sbirthdate)as'年龄'
from Student x,(select AVG(YEAR(GETDATE())-YEAR(sbirthdate))
from Student y
group by y.Smajor) as avg_sex(sex)
where YEAR(GETDATE())-YEAR(sbirthdate)>avg_sex.sex;
/*（4）查询学分大于"操作系统"的所有课程名称；*/
/*方法1：嵌套>*/
select Cname
from Course
where Ccredit >(select Ccredit
from Course
where Cname='操作系统');
/*方法2：嵌套exists*/
select Cname
from Course x
where exists(select *
from Course y
where x.Ccredit>y.Ccredit and y.Cname='操作系统');
/*（5）查询没有选"数据库"的学生学号；*/
/*方法1：嵌套exists*/
select distinct Sno
from SC x
where not exists(select *
from SC y
where y.Sno=x.Sno and exists(select *
from Course
where Cno=y.Cno and Cname='数据库系统概论') );
/*方法2：集合差*/
select distinct sno
from SC
except
select Sno
from Course,SC
where Course.Cno=SC.Cno and Cname='数据库系统概论';
/*方法3：not in*/
select distinct Sno
from SC
where Sno not in (select Sno
from SC
where Cno in (select Cno
from Course
where Cname='数据库系统概论') );
/*（6）查询与"数据库"、"数学"学分不同的所有课程名称；*/
/*方法1：not in*/
select Cname
from Course
where Ccredit not in (select Ccredit
from Course
where Cname in (select Cname
from Course
where Cname in('数据库系统概论','离散数学') ));
/*方法3：<> all或者any*/
select Cname
from Course
where Ccredit <> any(select Ccredit
from Course
where Cname in (select Cname
from Course
where Cname in('数据库系统概论','离散数学') ));
/*（7）查询平均分大于等于80分的所有课程号和课程名称；*/
/*方法1：连接查询*/
select Course.Cno,Cname
from Course,SC
where Course.Cno=SC.Cno
group by Course.Cno,Cname
having AVG(Grade)>='80';
/*方法2：派生表*/
select Course.Cno,Cname
from Course,(select cno
from SC
group by Cno
having AVG(Grade)>='80')as avg_sc(avg_cno)
where Course.Cno=avg_sc.avg_cno
group by Course.Cno,Cname
/*（8）查询同时选修了'81001'和'81002'号课程的学生学号和姓名；*/
/*方法1：自身连接*/
select student.Sno,Sname
from Student ,SC s1,SC s2
where Student.Sno=s1.Sno and s1.Sno=s2.Sno and s1.Cno='81001' and s2.Cno='81002'
group by Student.Sno,Sname;
/*方法2：嵌套in*/
select Sno,Sname
from Student
where Sno in (select Sno
from SC
where Cno = '81001'and Sno in (select Sno
from SC
where Cno='81002'));
/*方法3：集合*/
select student.Sno,Sname
from Student ,SC
where Student.Sno=sc.Sno and Cno='81001'
INTERSECT
select student.Sno,Sname
from Student ,SC
where Student.Sno=SC.Sno and Cno='81002';
/*（9）查询同时选修了'数据库系统概论'和'数据结构'的学生学号和姓名；*/
/*方法1：嵌套in*/
select Sno,Sname
from Student
where Sno in (select Sno
from SC
where Cno in (select Cno
from Course
where Cname = '数据库系统概论') and Sno in (select Sno
from SC
where Cno in (select Cno
from Course
where Cname='数据结构')));
/*方法2：集合*/
select Student.Sno,Sname
from Student,(select Sno
from SC
where Cno in (select Cno
from Course
where Cname = '数据库系统概论'))as x_sc(sno)
where Student.Sno=x_sc.sno
intersect
select Student.Sno,Sname
from Student,(select Sno
from SC
where Cno in (select Cno
from Course
where Cname='数据结构'))as y_sc(sno)
where Student.Sno=y_sc.sno
/*（10）查询所有学生都选了的课程号；*/ /*嵌套exists，不存在一个学生没选的课程*/
SELECT Cno
FROM Course
WHERE NOT EXISTS
(SELECT *
FROM Student
WHERE NOT EXISTS
(SELECT *
FROM SC
WHERE Sno= Student.Sno
AND Cno= Course.Cno
)
);
/*（11）查询与"数据结构"具有相同先修课的课程号和课程名；*/
/*方法1：自身连接*/
select c1.Cno,c1.Cname
from Course c1,Course c2
where c1.Cpno=c2.Cpno and c2.Cname='数据结构' and c1.Cname<>'数据结构';
/*方法2：嵌套in*/
select Cno,Cname
from Course
where Cname<>'数据结构' and Cpno in (select Cpno
from Course
where Cname='数据结构');
/*方法3：嵌套exists*/
select Cno,Cname
from Course x
where Cname<>'数据结构' and exists (select *
from Course y
where y.Cpno=x.Cpno and Cname='数据结构');
/*方法4：派生表*/
select Cno,Cname
from Course,(select Cpno
from Course
where Cname='数据结构')as xcourse(scpno)
where Cname<>'数据结构'and Cpno=xcourse.scpno;
/*（12）查询所有具有不及格记录的学生学号和姓名*/
/*方法1：连接查询*/
select Student.Sno,Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade
having Grade<'60';
/*方法3：嵌套in*/
select Sno,Sname
from Student
where Sno in (select Sno
from SC
where Grade<'60');
/*方法3：嵌套exists*/
select Sno,Sname
from Student
where exists(select *
from SC
where sno=Student.Sno and Grade<'60');
/*方法4：派生表*/
select Student.Sno,Sname
from Student,(select Sno
from SC
where Grade<'60')as xsc(sno)
where Student.Sno=xsc.sno
group by Student.Sno,Sname
/*（13）查询计算机科学与技术专业学生选修的所有课程号；*/
/*方法1：连接查询*/
select SC.Cno
from Student,SC
where Student.Sno=SC.Sno
group by SC.Cno,Smajor
having Smajor='计算机科学与技术';
/*方法2：嵌套in*/
select distinct Cno
from SC
where Sno in (select Sno
from Student
where Smajor='计算机科学与技术');
/*方法3：嵌套exists*/
select distinct Cno
from SC
where exists(select *
from Student
where Sno=SC.Sno and Smajor='计算机科学与技术');
/*方法4：派生表*/
select Cno
from SC,(select Sno
from Student
where Smajor='计算机科学与技术')as xstudent(sno)
where xstudent.sno=SC.Sno
group by Cno;
/*（14）查询所有计算机科学与技术专业学生都选的课程号；*/
SELECT Cno
FROM Course
WHERE NOT EXISTS
(SELECT *
FROM Student
WHERE NOT EXISTS
(SELECT *
FROM SC
WHERE Sno= Student.Sno
AND Cno= Course.Cno
)and Smajor='计算机科学与技术'
);
/*（15）查询选修了81003号课程并且不及格的学生姓名*/
/*方法1：多表连接法*/
select Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade,Cno
having Grade<'60'and Cno='81003';
/*方法2：嵌套in*/
select Sname
from Student
where Sno in (select Sno
from SC
where Grade<'60'and Cno='81003');
/*方法3：交集*/
select Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade,Cno
having Grade<'60'
intersect
select Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade,Cno
having Cno='81003';
/*方法4：派生表*/
select Sname
from Student,(select Sno
from SC
where Grade<'60'and Cno='81003')as xsc(sno)
where Student.Sno=xsc.sno
group by Sname;
/*方法5：嵌套exists*/
select Sname
from Student
where exists(select *
from SC
where Sno=Student.Sno and Grade<'60'and Cno='81003');
/*（16）查询选修了"数据库系统概论"并且不及格的学生姓名*/
/*方法1：多表连接法*/
select Sname
from Student,SC,Course
where Student.Sno=SC.Sno and SC.Cno=Course.Cno
group by Student.Sno,Sname,Grade,Cname
having Grade<'60'and Cname='数据库系统概论';
/*方法2：嵌套in*/
select Sname
from Student
where Sno in (select Sno
from SC
where Grade<'60'and Cno in (select Cno
from Course
where Cname='数据库系统概论'));
/*方法3：交集*/
select Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade
having Grade<'60'
intersect
select Sname
from Student,SC,Course
where Student.Sno=SC.Sno and SC.Cno=Course.Cno
group by Student.Sno,Sname,Cname
having Cname='数据库系统概论';
/*方法4：派生表*/
select Sname
from Student,(select Sno,Cno
from SC
where Grade<'60')as xsc(sno,cno),(select Cno
from Course
where Cname='数据库系统概论')as xcourse(cno)
where Student.Sno=xsc.sno and xsc.cno=xcourse.cno
group by Sname;
/*（17）查询计算机科学与技术专业选修了"数据库系统概论"课且成绩及格的所有学生的学号和姓名；*/
/*方法1：多表连接法*/
select Student.Sno,Sname
from Student,SC,Course
where Student.Sno=SC.Sno and SC.Cno=Course.Cno
group by Student.Sno,Sname,Grade,Cname,Smajor
having Grade>'60'and Cname='数据库系统概论'and Smajor='计算机科学与技术';
/*方法2：嵌套in*/
select Sno,Sname
from Student
where Smajor='计算机科学与技术' and Sno in (select Sno
from SC
where Grade>'60'and Cno in (select Cno
from Course
where Cname='数据库系统概论') );
/*方法3：交集*/
select Student.Sno,Sname
from Student,SC
where Student.Sno=SC.Sno
group by Student.Sno,Sname,Grade
having Grade>'60'
intersect
select Student.Sno,Sname
from Student,SC,Course
where Student.Sno=SC.Sno and SC.Cno=Course.Cno
group by Student.Sno,Sname,Grade,Cname,Smajor
having Cname='数据库系统概论'
intersect
select Sno,Sname
from Student
where Smajor='计算机科学与技术';
/*方法4：派生表*/
select Student.Sno,Sname
from Student,(select Sno,Cno
from SC
where Grade>'60')as xsc(sno,cno),(select Cno
from Course
where Cname='数据库系统概论')as xcourse(cno)
where Student.Sno=xsc.sno and xsc.cno=xcourse.cno and Smajor='计算机科学与技术'
group by Student.Sno,Sname;
/*（18）查询与"刘晨"同岁且不与"刘晨"在同一个系的学生学号与姓名；*/
/*方法1：嵌套in*/
select Sno,Sname
from Student
where Sname<>'刘晨' and YEAR(GETDATE())-YEAR(sbirthdate)in (select YEAR(GETDATE())-YEAR(sbirthdate)
from Student
where Sname='刘晨')and Smajor not in (select Smajor
from Student
where Sname='刘晨');
/*方法2：嵌套exists*/
select Sno,Sname
from Student x
where Sname<>'刘晨'
and exists(select *
from Student y
where YEAR(GETDATE())-YEAR(y.sbirthdate)=YEAR(GETDATE())-YEAR(x.sbirthdate)and y.Sname='刘晨')
and not exists(select *
from Student z
where z.Smajor=x.Smajor and z.Sname='刘晨');
/*方法3：派生表*/
select Student.Sno,Sname
from Student,(select Sno,YEAR(GETDATE())-YEAR(sbirthdate)
from Student
where Sname='刘晨')as ystudent(sno,sex),(select Sno,Smajor
from Student
where Sname='刘晨')as zstudent(sno,smajor)
where Sname<>'刘晨'and YEAR(GETDATE())-YEAR(sbirthdate)=ystudent.sex and Student.Smajor<>zstudent.smajor