sql語句-linq語言-lambda表示式對照
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 })
2、 查詢教師所有的單位即不重複的Depart列。 select distinct depart from teacher Linq: from t in Teachers.Distinct() select t.DEPART Lambda: Teachers.Distinct().Select( t => t.DEPART)
3、 查詢Student表的所有記錄。 select * from student Linq: from s in Students select s Lambda: Students.Select( s => s)
4、 查詢Score表中成績在60到80之間的所有記錄。 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、 查詢Score表中成績為85，86或88的記錄。 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()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，以二個主鍵於與一個主鍵進行Any from e in CustomerDemographics where !e.CustomerCustomerDemos.Any() select e from c in Categories where !c.Products.Any() select c
6、 查詢Student表中"95031"班或性別為"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"))
7、 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)
8、 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)
9、 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()
10、查詢Score表中的最高分的學生學號和課程號。 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） 運算子"=="無法應用於"string"和"System.Linq.IQueryable<string>"型別的運算元 解決： 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；如果該序列並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()
11、查詢'3-105'號課程的平均分。 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()
12、查詢Score表中至少有5名學生選修的並以3開頭的課程的平均分數。 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也可以這樣寫: s.CNO.StartsWith("3") or SqlMethods.Like(s.CNO,"%3")
13、查詢最低分大於70，最高分小於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 })
15、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 })
16、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 }