LINQ To SQL && Lambda 练习题 Part One

网上看人家的Sql练习题,我用以Linq to Sql ,Lambda两种写式翻译一下,供学习LINQ,Lambda的同志参考

颜色注释: SQL LinqToSql Lambda QA

1 查询Student表中的所有记录的SnameSsexClass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6080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858688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""的同学记录。
select * from student where class ='95031' or ssex= N'
'
Linq:
    from s in Students
    where s.CLASS == "95031"
       || s.CLASS == "
"
    select s
Lambda:
    Students.Where(s => ( s.CLASS == "95031" || s.CLASS == "
"))


7
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 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 ASClinq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""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90Sno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SnameCnoDegree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SnoCnameDegree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SnameCnameDegree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 }

/未完待续。。(一共43个)

 

posted @ 2008-11-09 00:25  RicoRui  阅读(4668)  评论(1编辑  收藏  举报