SQL、LINQ、Lambda 三種用法

SQL、LINQ、Lambda 三種用法
顔色注釋： SQL LinqToSql Lambda QA
1、 查詢Student表中的所有記錄的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
    })

、 查詢教師所有的機關即不重複的Depart列。
select distinct depart from teacher
Linq:
    from t in Teachers.Distinct()
    select t.DEPART
Lambda:
    Teachers.Distinct().Select( t => t.DEPART)
、 查詢Student表的所有記錄。
select * from student
Linq:
    from s in Students
    select s
Lambda:
    Students.Select( s => s)

、 查詢Score表中成績在到之間的所有記錄。
select * from score where degree between  and 
Linq:
    from s in Scores
    where s.DEGREE >=  && s.DEGREE < 
    select s
Lambda:
    Scores.Where( 
        s => (
                s.DEGREE >=  && s.DEGREE <  
             )
    )
、 查詢Score表中成績為，或的記錄。
select * from score where degree in (,,)
Linq:
In
    from s in Scores
    where (
            new decimal[]{,,}
          ).Contains(s.DEGREE)
    select s
Lambda:
    Scores.Where( s => new Decimal[] {,,}.Contains(s.DEGREE))
Not in
    from s in Scores
    where !(
            new decimal[]{,,}
          ).Contains(s.DEGREE)
    select s
Lambda:
    Scores.Where( s => !(new Decimal[]{,,}.Contains(s.DEGREE)))
    Any()應用：雙表進行Any時，必須是主鍵為(String)
    CustomerDemographics CustomerTypeID（String）
    CustomerCustomerDemos (CustomerID CustomerTypeID) (String)
    一個主鍵與二個主建進行Any(或者是一對一關鍵進行Any)
    不可，以二個主鍵于與一個主鍵進行Any

    from e in CustomerDemographics
    where !e.CustomerCustomerDemos.Any()
    select e

    from c in Categories
    where !c.Products.Any()
    select c
、 查詢Student表中"95031"班或性别為"女"的同學記錄。
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"))

、 以Class降序查詢Student表的所有記錄。
select * from student order by Class DESC
Linq:
    from s in Students
    orderby s.CLASS descending
    select s
Lambda:
    Students.OrderByDescending(s => s.CLASS)
、 以Cno升序、Degree降序查詢Score表的所有記錄。
select * from score order by Cno ASC,Degree DESC
Linq:(這裡Cno ASC在linq中要寫在最外面)
    from s in Scores
    orderby s.DEGREE descending
    orderby s.CNO ascending 
    select s
Lambda:
    Scores.OrderByDescending( s => s.DEGREE)
          .OrderBy( s => s.CNO)

、 查詢"95031"班的學生人數。
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()
、查詢Score表中的最高分的學生學号和課程号。
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()
操作時問題？執行時報錯： where s.SNO == sno（這行報出來的） 運算符"=="無法應用于"string"和"System.Linq.IQueryable<string>"類型的操作數
解決：
原：let sno = (from ss in Scores
                where ss.DEGREE == maxDegree
                select ss.SNO).ToString()
Queryable().Single()傳回序列的唯一進制素；如果該序列并非恰好包含一個元素，則會引發異常。 
解：let sno = (from ss in Scores
                where ss.DEGREE == maxDegree
                select ss.SNO).Single().ToString()
、查詢'3-105'号課程的平均分。
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()

、查詢Score表中至少有名學生選修的并以開頭的課程的平均分數。
select avg(degree) from score where cno like '3%' group by Cno having count(*)>=
Linq:
        from s in Scores
        where s.CNO.StartsWith("3")
        group s by s.CNO
        into cc
        where cc.Count() >= 
        select cc.Average( c => c.DEGREE)
Lambda:
    Scores.Where( s => s.CNO.StartsWith("3") )
            .GroupBy( s => s.CNO )
              .Where( cc => ( cc.Count() >= ) )
                .Select( cc => cc.Average( c => c.DEGREE) )
Linq: SqlMethod
like也可以這樣寫:
    s.CNO.StartsWith("3") or SqlMethods.Like(s.CNO,"%3")
、查詢最低分大于，最高分小于的Sno列。
select sno from score group by sno having min(degree) >  and max(degree) < 
Linq:
    from s in Scores
    group s by s.SNO
    into ss
    where ss.Min(cc => cc.DEGREE) >  && ss.Max( cc => cc.DEGREE) < 
    select new
    {
        sno = ss.Key
    }
Lambda:
    Scores.GroupBy (s => s.SNO)
               .Where (ss => ((ss.Min (cc => cc.DEGREE) > ) && (ss.Max (cc => cc.DEGREE) < )))
                   .Select ( ss => new {
                                        sno = ss.Key
                                     })
、查詢所有學生的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
                                          })
、查詢所有學生的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
                                        })
、查詢所有學生的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 }