1、 查询Student表中的所有记录的Sname、Ssex和Class列。
select sname,ssex,class from
student
Linq:
from s in Students
select new
{
s.SNAME,
s.SSEX,
s.CLASS
}
Lambda:
Students.Select( s => new
{
SNAME = s.SNAME,SSEX =
s.SSEX,CLASS = s.CLASS
})
2、 查询教师所有的单位即不重复的Depart列。
select distinct depart from
teacher
Linq:
from t in Teachers.Distinct()
select
t.DEPART
Lambda:
Teachers.Distinct().Select( t => t.DEPART)
3、 查询Student表的所有记录。
select * from student
Linq:
from s in Students
select s
Lambda:
Students.Select( s => s)
4、 查询Score表中成绩在60到80之间的所有记录。
select * from score where degree between
60 and 80
Linq:
from s in Scores
where s.DEGREE
>= 60 && s.DEGREE < 80
select s
Lambda:
Scores.Where(
s =>
(
s.DEGREE >= 60 && s.DEGREE <
80
)
)
5、 查询Score表中成绩为85，86或88的记录。
select * from score where degree in
(85,86,88)
Linq:
In
from s in Scores
where
(
new
decimal[]{85,86,88}
).Contains(s.DEGREE)
select s
Lambda:
Scores.Where( s => new Decimal[] {85,86,88}.Contains(s.DEGREE))
Not in
from s in Scores
where
!(
new
decimal[]{85,86,88}
).Contains(s.DEGREE)
select s
Lambda:
Scores.Where( s => !(new Decimal[]{85,86,88}.Contains(s.DEGREE)))
Any()应用：双表进行Any时，必须是主键为(String)
CustomerDemographics CustomerTypeID（String）
CustomerCustomerDemos (CustomerID CustomerTypeID) (String)
一个主键与二个主建进行Any(或者是一对一关键进行Any)
不可，以二个主键于与一个主键进行Any
from e in
CustomerDemographics
where
!e.CustomerCustomerDemos.Any()
select
e
from c in
Categories
where !c.Products.Any()
select c
6、 查询Student表中"95031"班或性别为"女"的同学记录。
select * from student where class
=‘95031‘ or ssex= N‘女‘
Linq:
from s in Students
where s.CLASS ==
"95031"
|| s.CLASS ==
"女"
select s
Lambda:
Students.Where(s => ( s.CLASS == "95031" || s.CLASS == "女"))
7、 以Class降序查询Student表的所有记录。
select * from student order by Class
DESC
Linq:
from s in Students
orderby s.CLASS
descending
select s
Lambda:
Students.OrderByDescending(s => s.CLASS)
8、 以Cno升序、Degree降序查询Score表的所有记录。
select * from score order by Cno
ASC,Degree DESC
Linq:(这里Cno ASC在linq中要写在最外面)
from s in Scores
orderby s.DEGREE
descending
orderby s.CNO
ascending
select s
Lambda:
Scores.OrderByDescending( s =>
s.DEGREE)
.OrderBy( s
=> s.CNO)
9、 查询"95031"班的学生人数。
select count(*) from student where class =
‘95031‘
Linq:
( from s in
Students
where s.CLASS ==
"95031"
select
s
).Count()
Lambda:
Students.Where( s => s.CLASS == "95031"
)
.Select( s =>
s)
.Count()
10、查询Score表中的最高分的学生学号和课程号。
select distinct s.Sno,c.Cno from student as
s,course as c ,score as sc
where s.sno=(select sno from score where
degree = (select max(degree) from score))
and c.cno = (select cno from score
where degree = (select max(degree) from score))
Linq:
(
from s in
Students
from c in
Courses
from sc in
Scores
let maxDegree = (from sss
in
Scores
select
sss.DEGREE
).Max()
let sno = (from ss in
Scores
where ss.DEGREE ==
maxDegree
select ss.SNO).Single().ToString()
let cno = (from ssss in
Scores
where ssss.DEGREE ==
maxDegree
select
ssss.CNO).Single().ToString()
where s.SNO == sno && c.CNO ==
cno
select new
{
s.SNO,
c.CNO
}
).Distinct()
操作时问题？执行时报错： where s.SNO == sno（这行报出来的）
运算符"=="无法应用于"string"和"System.Linq.IQueryable<string>"类型的操作数
解决：
原：let
sno = (from ss in
Scores
where ss.DEGREE ==
maxDegree
select
ss.SNO).ToString()
Queryable().Single()
返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。
解：let
sno = (from ss in
Scores
where ss.DEGREE ==
maxDegree
select ss.SNO).Single().ToString()
11、查询‘3-105‘号课程的平均分。
select avg(degree) from score where cno =
‘3-105‘
Linq:
(
from s in
Scores
where s.CNO ==
"3-105"
select
s.DEGREE
).Average()
Lambda:
Scores.Where( s => s.CNO ==
"3-105")
.Select( s =>
s.DEGREE)
.Average()
12、查询Score表中至少有5名学生选修的并以3开头的课程的平均分数。
select avg(degree) from score
where cno like ‘3%‘ group by Cno having count(*)>=5
Linq:
from s in
Scores
where
s.CNO.StartsWith("3")
group s by
s.CNO
into
cc
where cc.Count() >=
5
select cc.Average( c =>
c.DEGREE)
Lambda:
Scores.Where( s => s.CNO.StartsWith("3")
)
.GroupBy( s => s.CNO
)
.Where( cc => ( cc.Count() >= 5)
)
.Select( cc => cc.Average( c => c.DEGREE) )
Linq:
SqlMethod
like也可以这样写:
s.CNO.StartsWith("3") or SqlMethods.Like(s.CNO,"%3")
13、查询最低分大于70，最高分小于90的Sno列。
select sno from score group by sno having
min(degree) > 70 and max(degree) < 90
Linq:
from s in Scores
group s by
s.SNO
into ss
where ss.Min(cc =>
cc.DEGREE) > 70 && ss.Max( cc => cc.DEGREE) <
90
select new
{
sno =
ss.Key
}
Lambda:
Scores.GroupBy (s =>
s.SNO)
.Where (ss => ((ss.Min (cc => cc.DEGREE) > 70) && (ss.Max (cc
=> cc.DEGREE) <
90)))
.Select ( ss => new
{
sno =
ss.Key
})
14、查询所有学生的Sname、Cno和Degree列。
select s.sname,sc.cno,sc.degree from
student as s,score as sc where s.sno = sc.sno
Linq:
from s in Students
join sc in
Scores
on s.SNO equals sc.SNO
select
new
{
s.SNAME,
sc.CNO,
sc.DEGREE
}
Lambda:
Students.Join(Scores, s =>
s.SNO,
sc =>
sc.SNO,
(s,sc) =>
new{
SNAME =
s.SNAME,
CNO =
sc.CNO,
DEGREE =
sc.DEGREE
})
15、查询所有学生的Sno、Cname和Degree列。
select sc.sno,c.cname,sc.degree from
course as c,score as sc where c.cno = sc.cno
Linq:
from c in Courses
join sc in
Scores
on c.CNO equals sc.CNO
select
new
{
sc.SNO,c.CNAME,sc.DEGREE
}
Lambda:
Courses.Join ( Scores, c =>
c.CNO,
sc =>
sc.CNO,
(c, sc) =>
new
{
SNO =
sc.SNO,
CNAME =
c.CNAME,
DEGREE =
sc.DEGREE
})
16、查询所有学生的Sname、Cname和Degree列。
select s.sname,c.cname,sc.degree from
student as s,course as c,score as sc where s.sno = sc.sno and c.cno =
sc.cno
Linq:
from s in Students
from c in
Courses
from sc in Scores
where
s.SNO == sc.SNO && c.CNO == sc.CNO
select new {
s.SNAME,c.CNAME,sc.DEGREE }
