这里我们建几个SQL表，我们用个图来说明关系
这里tid的值和教师表中的id相匹配，pid和院系表中的id相匹配,也就是说这样建表就把三张表的关系给建立起来了。学生表在最低层，院系表在最高层。
而这里我们就要讲一个
外键
的概念：外键是作为与主表的主键相关联的键值，外键可以有多个，同时有外键的表称作对应主键所在表的从表，那主键所在的表就作主表。图中，
tid是教师表中id的外键，也就学生表是教师表的从表，同理，教师表也就是院系表的从表。
外键的主要作用是保持数据一致性，完整性，主要目的是控制存储在外键表中的数据。
当然在这时我们还不需要去建立真正的外键联系关系
现在我们要查询学生表，教师表，院系表的所有信息：
select * from student,teacher,part
//查询这三个表中的所有信息
我们现在要查询某学生的教师是的名字：
select teaname from student,teacher where (student.id =”) and (teacher.id = student.tid)
//这里有两个约束条件，一个是约束学生的id号，一个是约束学生表和教师表的数据要相对应，也就是，这样查询的结果，就是该学生tid所对应教师表中id号的teaname字段的数据，也就是这位学生的教师名字了
现在有一个问题，我想问这个学生所在院系是什么？这个问题就应该迎刃而解了吧。
当然这只是简单的多表查询，其实在真正多表查询时，是用的以下方法：
这里讲一个join方法
该语句是实现多对对查询或一对一查询的方法，当我们在用简单多表查询的时候，它的匹配是无逻辑的，也就是没有具体的约束条件，它不会按照逻辑关系来约束。有可能这个学生会和一个无关第教师联系起来，或者和一个无关的院系联系起来。
我们用一个简单的join方法查询：
select teacher.teaname from student join teacher on(student.tid = teacher.id)where (student.id=’1′)
//查询id号为1的学生的教师的名字
这就是join语句的语法，它是个嵌套语句，也就是把一个表嵌套在另一个表中，一般都是自下而上的嵌套，如上例，就是学生表去加入教师表的集合。也就是从表加入主表。
这种join有两个参数，我们上例用的是缺省参数–
innor
,当我们直接用join时，就默认是这个参数，还有一个
left
，这两个参数在用时有很大的区别。
select * from student left join teacher on(student.tid = teacher.id)
这上面这个例子中，用left和不用left参数是有很大区别的。用如果在学生表中，有几个新报道的学生还未分配教师，那么，用left参数查询的时候也会显示出来，尽管他的tid为空，和教师表中的数据不匹配，但也会显示出来。
若不用left ，那么就不会显示这几个新学生。
通过这个例子应该能更好的理解left的用处了吧，在处理中，我们要根据需求来进行设计查询语句。
当然，我们先前讲的外键这个时候我们也需要拿出来用了。下图所示：
我们现在建好了这个表，我们有如下设计需求，当我在删掉这个类别的时候，我们需要把该类别下的产品也删掉。我们可以用最原始的方法，也就是先查询所有该类别的产品，然后把类别下的产品全删完后才删除该类别，但这样，不显得很麻烦吗？
这里就该用上外键的功能了，首先我们建立好外键，也就是把cid设为类别表中id的外键
ALTER TABLE product ADD CONSTRAINT fk_product_cid
FOREIGN KEY (cid)
REFERENCES category(id);
//第一行是在product(产品表)中添加一个外键，第二行是此外键对应的字段是cid，第三行是此外键对应的键值为category(类别表)中的id.
那么这就建立好了外键的关系，但是这样还是不行，我们还需要了解一下外键的级联操作的相关信息：
CASCADE（连锁关系，当主表变更，从表的相应信息也会变更）
RESTRICT(禁止主表变更)
SET NULL(子表相应字段设置为空)
。。。。。
一般我们用的最多的是连锁关系，而上例所讲的设计我们就需要用到连锁关系：
ALTER TABLE product ADD CONSTRAINT fk_product_cid
FOREIGN KEY (cid)
REFERENCES category(id);
ON UPDATE CASCADE;
ON DELETE CASCADE;
//这就实现了更新的连锁和删除的连锁。也就是当主表的信息变更，从表的相关信息也会变更。当主表的信息删除，从表的相关联信息也会删除
——————————————————————————————————————————————–
问题及描述：
–1.学生表
Student(S#,Sname,Sage,Ssex) –S# 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别
–2.课程表
Course(C#,Cname,T#) –C# –课程编号,Cname 课程名称,T# 教师编号
–3.教师表
Teacher(T#,Tname) –T# 教师编号,Tname 教师姓名
–4.成绩表
SC(S#,C#,score) –S# 学生编号,C# 课程编号,score 分数
*/
—
创建测试数据
create
table
Student(S#
varchar
(
10
),Sname
nvarchar
(
10
),Sage
datetime
,Ssex
nvarchar
(
10
))
insert
into
Student
values
(
‘
01
‘
, N
‘
赵雷
‘
,
‘
1990-01-01
‘
, N
‘
男
‘
)
insert
into
Student
values
(
‘
02
‘
, N
‘
钱电
‘
,
‘
1990-12-21
‘
, N
‘
男
‘
)
insert
into
Student
values
(
‘
03
‘
, N
‘
孙风
‘
,
‘
1990-05-20
‘
, N
‘
男
‘
)
insert
into
Student
values
(
‘
04
‘
, N
‘
李云
‘
,
‘
1990-08-06
‘
, N
‘
男
‘
)
insert
into
Student
values
(
‘
05
‘
, N
‘
周梅
‘
,
‘
1991-12-01
‘
, N
‘
女
‘
)
insert
into
Student
values
(
‘
06
‘
, N
‘
吴兰
‘
,
‘
1992-03-01
‘
, N
‘
女
‘
)
insert
into
Student
values
(
‘
07
‘
, N
‘
郑竹
‘
,
‘
1989-07-01
‘
, N
‘
女
‘
)
insert
into
Student
values
(
‘
08
‘
, N
‘
王菊
‘
,
‘
1990-01-20
‘
, N
‘
女
‘
)
create
table
Course(C#
varchar
(
10
),Cname
nvarchar
(
10
),T#
varchar
(
10
))
insert
into
Course
values
(
‘
01
‘
, N
‘
语文
‘
,
‘
02
‘
)
insert
into
Course
values
(
‘
02
‘
, N
‘
数学
‘
,
‘
01
‘
)
insert
into
Course
values
(
‘
03
‘
, N
‘
英语
‘
,
‘
03
‘
)
create
table
Teacher(T#
varchar
(
10
),Tname
nvarchar
(
10
))
insert
into
Teacher
values
(
‘
01
‘
, N
‘
张三
‘
)
insert
into
Teacher
values
(
‘
02
‘
, N
‘
李四
‘
)
insert
into
Teacher
values
(
‘
03
‘
, N
‘
王五
‘
)
create
table
SC(S#
varchar
(
10
),C#
varchar
(
10
),score
decimal
(
18
,
1
))
insert
into
SC
values
(
‘
01
‘
,
‘
01
‘
,
80
)
insert
into
SC
values
(
‘
01
‘
,
‘
02
‘
,
90
)
insert
into
SC
values
(
‘
01
‘
,
‘
03
‘
,
99
)
insert
into
SC
values
(
‘
02
‘
,
‘
01
‘
,
70
)
insert
into
SC
values
(
‘
02
‘
,
‘
02
‘
,
60
)
insert
into
SC
values
(
‘
02
‘
,
‘
03
‘
,
80
)
insert
into
SC
values
(
‘
03
‘
,
‘
01
‘
,
80
)
insert
into
SC
values
(
‘
03
‘
,
‘
02
‘
,
80
)
insert
into
SC
values
(
‘
03
‘
,
‘
03
‘
,
80
)
insert
into
SC
values
(
‘
04
‘
,
‘
01
‘
,
50
)
insert
into
SC
values
(
‘
04
‘
,
‘
02
‘
,
30
)
insert
into
SC
values
(
‘
04
‘
,
‘
03
‘
,
20
)
insert
into
SC
values
(
‘
05
‘
,
‘
01
‘
,
76
)
insert
into
SC
values
(
‘
05
‘
,
‘
02
‘
,
87
)
insert
into
SC
values
(
‘
06
‘
,
‘
01
‘
,
31
)
insert
into
SC
values
(
‘
06
‘
,
‘
03
‘
,
34
)
insert
into
SC
values
(
‘
07
‘
,
‘
02
‘
,
89
)
insert
into
SC
values
(
‘
07
‘
,
‘
03
‘
,
98
)
go
—
1、查询”01″课程比”02″课程成绩高的学生的信息及课程分数
—
1.1、查询同时存在”01″课程和”02″课程的情况
select
a.
*
, b.score
[
课程’01’的分数
]
,c.score
[
课程’02’的分数
]
from
Student a , SC b , SC c
where
a.S#
=
b.S#
and
a.S#
=
c.S#
and
b.C#
=
‘
01
‘
and
c.C#
=
‘
02
‘
and
b.score
>
c.score
—
1.2、查询同时存在”01″课程和”02″课程的情况和存在”01″课程但可能不存在”02″课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)
select
a.
*
, b.score
[
课程”01″的分数
]
,c.score
[
课程”02″的分数
]
from
Student a
left
join
SC b
on
a.S#
=
b.S#
and
b.C#
=
‘
01
‘
left
join
SC c
on
a.S#
=
c.S#
and
c.C#
=
‘
02
‘
where
b.score
>
isnull
(c.score,
0
)
—
2、查询”01″课程比”02″课程成绩低的学生的信息及课程分数
—
2.1、查询同时存在”01″课程和”02″课程的情况
select
a.
*
, b.score
[
课程’01’的分数
]
,c.score
[
课程’02’的分数
]
from
Student a , SC b , SC c
where
a.S#
=
b.S#
and
a.S#
=
c.S#
and
b.C#
=
‘
01
‘
and
c.C#
=
‘
02
‘
and
b.score
<
c.score
—
2.2、查询同时存在”01″课程和”02″课程的情况和不存在”01″课程但存在”02″课程的情况
select
a.
*
, b.score
[
课程”01″的分数
]
,c.score
[
课程”02″的分数
]
from
Student a
left
join
SC b
on
a.S#
=
b.S#
and
b.C#
=
‘
01
‘
left
join
SC c
on
a.S#
=
c.S#
and
c.C#
=
‘
02
‘
where
isnull
(b.score,
0
)
<
c.score
—
3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩
select
a.S# , a.Sname ,
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)) avg_score
from
Student a , sc b
where
a.S#
=
b.S#
group
by
a.S# , a.Sname
having
cast
(
avg
(b.score)
as
decimal
(
18
,
2
))
>=
60
order
by
a.S#
—
4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩
—
4.1、查询在sc表存在成绩的学生信息的SQL语句。
select
a.S# , a.Sname ,
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)) avg_score
from
Student a , sc b
where
a.S#
=
b.S#
group
by
a.S# , a.Sname
having
cast
(
avg
(b.score)
as
decimal
(
18
,
2
))
<
60
order
by
a.S#
—
4.2、查询在sc表中不存在成绩的学生信息的SQL语句。
select
a.S# , a.Sname ,
isnull
(
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)),
0
) avg_score
from
Student a
left
join
sc b
on
a.S#
=
b.S#
group
by
a.S# , a.Sname
having
isnull
(
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)),
0
)
<
60
order
by
a.S#
—
5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩
—
5.1、查询所有有成绩的SQL。
select
a.S#
[
学生编号
]
, a.Sname
[
学生姓名
]
,
count
(b.C#) 选课总数,
sum
(score)
[
所有课程的总成绩
]
from
Student a , SC b
where
a.S#
=
b.S#
group
by
a.S#,a.Sname
order
by
a.S#
—
5.2、查询所有(包括有成绩和无成绩)的SQL。
select
a.S#
[
学生编号
]
, a.Sname
[
学生姓名
]
,
count
(b.C#) 选课总数,
sum
(score)
[
所有课程的总成绩
]
from
Student a
left
join
SC b
on
a.S#
=
b.S#
group
by
a.S#,a.Sname
order
by
a.S#
—
6、查询”李”姓老师的数量
—
方法1
select
count
(Tname)
[
“李”姓老师的数量
]
from
Teacher
where
Tname
like
N
‘
李%
‘
—
方法2
select
count
(Tname)
[
“李”姓老师的数量
]
from
Teacher
where
left
(Tname,
1
)
=
N
‘
李
‘
—
7、查询学过”张三”老师授课的同学的信息
select
distinct
Student.
*
from
Student , SC , Course , Teacher
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
Course.T#
=
Teacher.T#
and
Teacher.Tname
=
N
‘
张三
‘
order
by
Student.S#
—
8、查询没学过”张三”老师授课的同学的信息
select
m.
*
from
Student m
where
S#
not
in
(
select
distinct
SC.S#
from
SC , Course , Teacher
where
SC.C#
=
Course.C#
and
Course.T#
=
Teacher.T#
and
Teacher.Tname
=
N
‘
张三
‘
)
order
by
m.S#
—
9、查询学过编号为”01″并且也学过编号为”02″的课程的同学的信息
—
方法1
select
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
and
SC.C#
=
‘
01
‘
and
exists
(
Select
1
from
SC SC_2
where
SC_2.S#
=
SC.S#
and
SC_2.C#
=
‘
02
‘
)
order
by
Student.S#
—
方法2
select
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
and
SC.C#
=
‘
02
‘
and
exists
(
Select
1
from
SC SC_2
where
SC_2.S#
=
SC.S#
and
SC_2.C#
=
‘
01
‘
)
order
by
Student.S#
—
方法3
select
m.
*
from
Student m
where
S#
in
(
select
S#
from
(
select
distinct
S#
from
SC
where
C#
=
‘
01
‘
union
all
select
distinct
S#
from
SC
where
C#
=
‘
02
‘
) t
group
by
S#
having
count
(
1
)
=
2
)
order
by
m.S#
—
10、查询学过编号为”01″但是没有学过编号为”02″的课程的同学的信息
—
方法1
select
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
and
SC.C#
=
‘
01
‘
and
not
exists
(
Select
1
from
SC SC_2
where
SC_2.S#
=
SC.S#
and
SC_2.C#
=
‘
02
‘
)
order
by
Student.S#
—
方法2
select
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
and
SC.C#
=
‘
01
‘
and
Student.S#
not
in
(
Select
SC_2.S#
from
SC SC_2
where
SC_2.S#
=
SC.S#
and
SC_2.C#
=
‘
02
‘
)
order
by
Student.S#
—
11、查询没有学全所有课程的同学的信息
—
11.1、
select
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
group
by
Student.S# , Student.Sname , Student.Sage , Student.Ssex
having
count
(C#)
<
(
select
count
(C#)
from
Course)
—
11.2
select
Student.
*
from
Student
left
join
SC
on
Student.S#
=
SC.S#
group
by
Student.S# , Student.Sname , Student.Sage , Student.Ssex
having
count
(C#)
<
(
select
count
(C#)
from
Course)
—
12、查询至少有一门课与学号为”01″的同学所学相同的同学的信息
select
distinct
Student.
*
from
Student , SC
where
Student.S#
=
SC.S#
and
SC.C#
in
(
select
C#
from
SC
where
S#
=
‘
01
‘
)
and
Student.S#
<>
‘
01
‘
—
13、查询和”01″号的同学学习的课程完全相同的其他同学的信息
select
Student.
*
from
Student
where
S#
in
(
select
distinct
SC.S#
from
SC
where
S#
<>
‘
01
‘
and
SC.C#
in
(
select
distinct
C#
from
SC
where
S#
=
‘
01
‘
)
group
by
SC.S#
having
count
(
1
)
=
(
select
count
(
1
)
from
SC
where
S#
=
‘
01
‘
))
—
14、查询没学过”张三”老师讲授的任一门课程的学生姓名
select
student.
*
from
student
where
student.S#
not
in
(
select
distinct
sc.S#
from
sc , course , teacher
where
sc.C#
=
course.C#
and
course.T#
=
teacher.T#
and
teacher.tname
=
N
‘
张三
‘
)
order
by
student.S#
—
15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
select
student.S# , student.sname ,
cast
(
avg
(score)
as
decimal
(
18
,
2
)) avg_score
from
student , sc
where
student.S#
=
SC.S#
and
student.S#
in
(
select
S#
from
SC
where
score
<
60
group
by
S#
having
count
(
1
)
>=
2
)
group
by
student.S# , student.sname
—
16、检索”01″课程分数小于60，按分数降序排列的学生信息
select
student.
*
, sc.C# , sc.score
from
student , sc
where
student.S#
=
SC.S#
and
sc.score
<
60
and
sc.C#
=
‘
01
‘
order
by
sc.score
desc
—
17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
—
17.1 SQL 2000 静态
select
a.S# 学生编号 , a.Sname 学生姓名 ,
max
(
case
c.Cname
when
N
‘
语文
‘
then
b.score
else
null
end
)
[
语文
]
,
max
(
case
c.Cname
when
N
‘
数学
‘
then
b.score
else
null
end
)
[
数学
]
,
max
(
case
c.Cname
when
N
‘
英语
‘
then
b.score
else
null
end
)
[
英语
]
,
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)) 平均分
from
Student a
left
join
SC b
on
a.S#
=
b.S#
left
join
Course c
on
b.C#
=
c.C#
group
by
a.S# , a.Sname
order
by
平均分
desc
—
17.2 SQL 2000 动态
declare
@sql
nvarchar
(
4000
)
set
@sql
=
‘
select a.S#
‘
+
N
‘
学生编号
‘
+
‘
, a.Sname
‘
+
N
‘
学生姓名
‘
select
@sql
=
@sql
+
‘
,max(case c.Cname when N
”’
+
Cname
+
”’
then b.score else null end) [
‘
+
Cname
+
‘
]
‘
from
(
select
distinct
Cname
from
Course)
as
t
set
@sql
=
@sql
+
‘
, cast(avg(b.score) as decimal(18,2))
‘
+
N
‘
平均分
‘
+
‘
from Student a left join SC b on a.S# = b.S# left join Course c on b.C# = c.C#
group by a.S# , a.Sname order by
‘
+
N
‘
平均分
‘
+
‘
desc
‘
exec
(
@sql
)
—
24、查询学生平均成绩及其名次
—
24.1 查询学生的平均成绩并进行排名，sql 2000用子查询完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。
select
t1.
*
, px
=
(
select
count
(
1
)
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t2
where
平均成绩
>
t1.平均成绩)
+
1
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t1
order
by
px
select
t1.
*
, px
=
(
select
count
(
distinct
平均成绩)
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t2
where
平均成绩
>=
t1.平均成绩)
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t1
order
by
px
—
24.2 查询学生的平均成绩并进行排名，sql 2005用rank,DENSE_RANK完成，分平均成绩重复时保留名次空缺和不保留名次空缺两种。
select
t.
*
, px
=
rank()
over
(
order
by
[
平均成绩
]
desc
)
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t
order
by
px
select
t.
*
, px
=
DENSE_RANK()
over
(
order
by
[
平均成绩
]
desc
)
from
(
select
m.S#
[
学生编号
]
,
m.Sname
[
学生姓名
]
,
isnull
(
cast
(
avg
(score)
as
decimal
(
18
,
2
)),
0
)
[
平均成绩
]
from
Student m
left
join
SC n
on
m.S#
=
n.S#
group
by
m.S# , m.Sname
) t
order
by
px
—
25、查询各科成绩前三名的记录
—
25.1 分数重复时保留名次空缺
select
m.
*
, n.C# , n.score
from
Student m, SC n
where
m.S#
=
n.S#
and
n.score
in
(
select
top
3
score
from
sc
where
C#
=
n.C#
order
by
score
desc
)
order
by
n.C# , n.score
desc
—
25.2 分数重复时不保留名次空缺，合并名次
—
sql 2000用子查询实现
select
*
from
(
select
t.
*
, px
=
(
select
count
(
distinct
score)
from
SC
where
C#
=
t.C#
and
score
>=
t.score)
from
sc t) m
where
px
between
1
and
3
order
by
m.c# , m.px
—
sql 2005用DENSE_RANK实现
select
*
from
(
select
t.
*
, px
=
DENSE_RANK()
over
(partition
by
c#
order
by
score
desc
)
from
sc t) m
where
px
between
1
and
3
order
by
m.C# , m.px
—
26、查询每门课程被选修的学生数
select
c# ,
count
(S#)
[
学生数
]
from
sc
group
by
C#
—
27、查询出只有两门课程的全部学生的学号和姓名
select
Student.S# , Student.Sname
from
Student , SC
where
Student.S#
=
SC.S#
group
by
Student.S# , Student.Sname
having
count
(SC.C#)
=
2
order
by
Student.S#
—
28、查询男生、女生人数
select
count
(Ssex)
as
男生人数
from
Student
where
Ssex
=
N
‘
男
‘
select
count
(Ssex)
as
女生人数
from
Student
where
Ssex
=
N
‘
女
‘
select
sum
(
case
when
Ssex
=
N
‘
男
‘
then
1
else
0
end
)
[
男生人数
]
,
sum
(
case
when
Ssex
=
N
‘
女
‘
then
1
else
0
end
)
[
女生人数
]
from
student
select
case
when
Ssex
=
N
‘
男
‘
then
N
‘
男生人数
‘
else
N
‘
女生人数
‘
end
[
男女情况
]
,
count
(
1
)
[
人数
]
from
student
group
by
case
when
Ssex
=
N
‘
男
‘
then
N
‘
男生人数
‘
else
N
‘
女生人数
‘
end
—
29、查询名字中含有”风”字的学生信息
select
*
from
student
where
sname
like
N
‘
%风%
‘
select
*
from
student
where
charindex
(N
‘
风
‘
, sname)
>
0
—
30、查询同名同性学生名单，并统计同名人数
select
Sname
[
学生姓名
]
,
count
(
*
)
[
人数
]
from
Student
group
by
Sname
having
count
(
*
)
>
1
—
31、查询1990年出生的学生名单(注：Student表中Sage列的类型是datetime)
select
*
from
Student
where
year
(sage)
=
1990
select
*
from
Student
where
datediff
(yy,sage,
‘
1990-01-01
‘
)
=
0
select
*
from
Student
where
datepart
(yy,sage)
=
1990
select
*
from
Student
where
convert
(
varchar
(
4
),sage,
120
)
=
‘
1990
‘
—
32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列
select
m.C# , m.Cname ,
cast
(
avg
(n.score)
as
decimal
(
18
,
2
)) avg_score
from
Course m, SC n
where
m.C#
=
n.C#
group
by
m.C# , m.Cname
order
by
avg_score
desc
, m.C#
asc
—
33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩
select
a.S# , a.Sname ,
cast
(
avg
(b.score)
as
decimal
(
18
,
2
)) avg_score
from
Student a , sc b
where
a.S#
=
b.S#
group
by
a.S# , a.Sname
having
cast
(
avg
(b.score)
as
decimal
(
18
,
2
))
>=
85
order
by
a.S#
—
34、查询课程名称为”数学”，且分数低于60的学生姓名和分数
select
sname , score
from
Student , SC , Course
where
SC.S#
=
Student.S#
and
SC.C#
=
Course.C#
and
Course.Cname
=
N
‘
数学
‘
and
score
<
60
—
35、查询所有学生的课程及分数情况；
select
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
order
by
Student.S# , SC.C#
—
36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数；
select
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
SC.score
>=
70
order
by
Student.S# , SC.C#
—
37、查询不及格的课程
select
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
SC.score
<
60
order
by
Student.S# , SC.C#
—
38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名；
select
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
SC.C#
=
‘
01
‘
and
SC.score
>=
80
order
by
Student.S# , SC.C#
—
39、求每门课程的学生人数
select
Course.C# , Course.Cname ,
count
(
*
)
[
学生人数
]
from
Course , SC
where
Course.C#
=
SC.C#
group
by
Course.C# , Course.Cname
order
by
Course.C# , Course.Cname
—
40、查询选修”张三”老师所授课程的学生中，成绩最高的学生信息及其成绩
—
40.1 当最高分只有一个时
select
top
1
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course , Teacher
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
Course.T#
=
Teacher.T#
and
Teacher.Tname
=
N
‘
张三
‘
order
by
SC.score
desc
—
40.2 当最高分出现多个时
select
Student.
*
, Course.Cname , SC.C# , SC.score
from
Student, SC , Course , Teacher
where
Student.S#
=
SC.S#
and
SC.C#
=
Course.C#
and
Course.T#
=
Teacher.T#
and
Teacher.Tname
=
N
‘
张三
‘
and
SC.score
=
(
select
max
(SC.score)
from
SC , Course , Teacher
where
SC.C#
=
Course.C#
and
Course.T#
=
Teacher.T#
and
Teacher.Tname
=
N
‘
张三
‘
)
—
41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
—
方法1
select
m.
*
from
SC m ,(
select
C# , score
from
SC
group
by
C# , score
having
count
(
1
)
>
1
) n
where
m.C#
=
n.C#
and
m.score
=
n.score
order
by
m.C# , m.score , m.S#
—
方法2
select
m.
*
from
SC m
where
exists
(
select
1
from
(
select
C# , score
from
SC
group
by
C# , score
having
count
(
1
)
>
1
) n
where
m.C#
=
n.C#
and
m.score
=
n.score)
order
by
m.C# , m.score , m.S#
—
42、查询每门功成绩最好的前两名
select
t.
*
from
sc t
where
score
in
(
select
top
2
score
from
sc
where
C#
=
T.C#
order
by
score
desc
)
order
by
t.C# , t.score
desc
—
43、统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
select
Course.C# , Course.Cname ,
count
(
*
)
[
学生人数
]
from
Course , SC
where
Course.C#
=
SC.C#
group
by
Course.C# , Course.Cname
having
count
(
*
)
>=
5
order
by
[
学生人数
]
desc
, Course.C#
—
44、检索至少选修两门课程的学生学号
select
student.S# , student.Sname
from
student , SC
where
student.S#
=
SC.S#
group
by
student.S# , student.Sname
having
count
(
1
)
>=
2
order
by
student.S#
—
45、查询选修了全部课程的学生信息
—
方法1 根据数量来完成
select
student.
*
from
student
where
S#
in
(
select
S#
from
sc
group
by
S#
having
count
(
1
)
=
(
select
count
(
1
)
from
course))
—
方法2 使用双重否定来完成
select
t.
*
from
student t
where
t.S#
not
in
(
select
distinct
m.S#
from
(
select
S# , C#
from
student , course
) m
where
not
exists
(
select
1
from
sc n
where
n.S#
=
m.S#
and
n.C#
=
m.C#)
)
—
方法3 使用双重否定来完成
select
t.
*
from
student t
where
not
exists
(
select
1
from
(
select
distinct
m.S#
from
(
select
S# , C#
from
student , course
) m
where
not
exists
(
select
1
from
sc n
where
n.S#
=
m.S#
and
n.C#
=
m.C#)
) k
where
k.S#
=
t.S#
)
—
46、查询各学生的年龄
—
46.1 只按照年份来算
select
*
,
datediff
(yy , sage ,
getdate
())
[
年龄
]
from
student
—
46.2 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
select
*
,
case
when
right
(
convert
(
varchar
(
10
),
getdate
(),
120
),
5
)
<
right
(
convert
(
varchar
(
10
),sage,
120
),
5
)
then
datediff
(yy , sage ,
getdate
())
–
1
else
datediff
(yy , sage ,
getdate
())
end
[
年龄
]
from
student
—
47、查询本周过生日的学生
select
*
from
student
where
datediff
(week,
datename
(yy,
getdate
())
+
right
(
convert
(
varchar
(
10
),sage,
120
),
6
),
getdate
())
=
0
—
48、查询下周过生日的学生
select
*
from
student
where
datediff
(week,
datename
(yy,
getdate
())
+
right
(
convert
(
varchar
(
10
),sage,
120
),
6
),
getdate
())
=
–
1
—
49、查询本月过生日的学生
select
*
from
student
where
datediff
(mm,
datename
(yy,
getdate
())
+
right
(
convert
(
varchar
(
10
),sage,
120
),
6
),
getdate
())
=
0
—
50、查询下月过生日的学生
select
*
from
student
where
datediff
(mm,
datename
(yy,
getdate
())
+
right
(
convert
(
varchar
(
10
),sage,
120
),
6
),
getdate
())
=
–
1
drop
table
Student,Course,Teacher,SC