sql语句-linq语言-lambda表达式对照 （赞）

原文出处：http://blog.csdn.net/swarb/article/details/8206976

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 }