sql语句-linq语言-lambda表达式对照

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 }