.NET基础学习(LINQ)(2)

2、join子句

LINQ中的join子句和SQL中的join很相似，连接操作接受两个集合然后创建一个临时的对象集合，每个对象包含原始集合对象中的所有字段，使用连接来结合两个或更多个集合中的数据。
示例代码如下：

 1  public class Student
 2  {
 3     public int StID;
 4     public string LastName;
 5  }
 6  public class CourseStudent
 7  {
 8     public string CourseName;
 9     public int StID;
10  }
11
12  CourseStudent[] studentInCourses = new CourseStudent[]{
13                  new CourseStudent{CourseName="Art",StID=1},
14                  new CourseStudent{CourseName="Art",StID=3},
15                  new CourseStudent{CourseName="History",StID=1},
16                  new CourseStudent{CourseName="History",StID=2},
17                  new CourseStudent{CourseName="Physics",StID=3}
18                 };
19  Student[] students = new Student[] {
20            new Student{StID=1,LastName="张三"},
21            new Student{StID=2,LastName="李四"},
22            new Student{StID=3,LastName="王五"}
23            };
24
25  //获取选修2门课以上同学的名字
26  var query = (from s in students
27               join c in studentInCourses on s.StID equals c.StID
28               where (from x in studentInCourses where x.StID==c.StID select x.StID).Count()>1
29               select s.LastName).Distinct();
30  foreach (var v in query) Console.Write("{0}\t",v);
31  Console.WriteLine("");
32             //获取选修历史同学的名字
33  var query1 = from s in students