LINQ的書寫格式如下： 　 　from 臨時變數 in 集合物件或資料庫物件 　 　where 條件表示式 　　 [order by條件] 　　 select 臨時變數中被查詢的值 　 　[group by 條件]

Lambda表示式的書寫格式如下：

(引數列表) => 表示式或者語句塊

其中： 引數個數：可以有多個引數，一個引數，或者無引數。

引數型別：可以隱式或者顯式定義。

表示式或者語句塊：這部分就是我們平常寫函式的實現部分（函式體）。

1.查詢全部

複製程式碼 例項 Code 查詢Student表的所有記錄。 select * from student Linq: from s in Students select s Lambda: Students.Select( s => s) 複製程式碼 2 按條件查詢全部：

複製程式碼 例項 Code 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 }) 複製程式碼 3.distinct 去掉重複的

複製程式碼 例項 Code 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) 複製程式碼 4.連線查詢 between and

複製程式碼 例項 Code 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 ) ) 複製程式碼 5.在範圍內篩選 In

複製程式碼 例項 Code select * from score where degree in (85,86,88) Linq: 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)) 複製程式碼 6.or 條件過濾

複製程式碼 例項 Code 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”)) 複製程式碼 7.排序

複製程式碼 例項 Code 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) 複製程式碼 8.count（）行數查詢

複製程式碼 例項 Code 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() 複製程式碼 10.avg()平均

複製程式碼 例項 Code 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) 複製程式碼 11.子查詢

複製程式碼 例項 Code 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() 複製程式碼 12.分組 過濾

複製程式碼 例項 Code 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") 複製程式碼 13.分組

複製程式碼 例項 Code 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") 複製程式碼 14. 多表查詢

按 Ctrl+C 複製程式碼

例項 Code 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 }) .Average() 按 Ctrl+C 複製程式碼