c#中LINQ的基本用法实例

using System;
using System.Collections.Generic;
using System.Linq;

namespace LINK查询
{
 class Program
 {
 static void Main(string[] args)
 {
  int[] number = { 2, 4, 6, 8, 10 };　//获取数据源
  IEnumerable lowNum = from n in number //创建并存储查询，不会执行操作
     where n <8
     select n;

  foreach(var val in lowNum) //执行查询
  {
  Console.Write("{0} ", val);
  }

  Console.ReadKey();
 }
 }
}

from Type Item in Items

var query = from s in students
  join c in course on s.SID equals c.SID

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LINK查询
{
 class Program
 {
 public class Student //声明student类
 {
  public int stId; //学生ID
  public string stuName; //学生姓名
 }

 public class Course //声明course类
 {
  public int stId; //学生ID
  public string courseName; //课程名
 }

 static Student[] students = new Student[]
 {
  new Student {stId = 1,stuName = "jack"},
  new Student {stId = 2,stuName = "taylor"},
  new Student {stId = 3,stuName = "fleming"}
 };

 static Course[] courses = new Course[]
 {
  new Course{stId = 1,courseName = "art"},
  new Course{stId = 2, courseName = "art"},
  new Course{stId = 1,courseName = "history"},
  new Course{stId = 3, courseName = "history"},
  new Course{stId = 3,courseName = "physics"},
 };

 static void Main(string[] args)
 { 
  //查询所有选修了history课的学生名
  var query = from s in students
   join c in courses on s.stId equals c.stId
   where c.courseName == "history"
   select s.stuName;

  foreach(string str in query)
  {
  Console.Write("{0} ", str);
  }
  Console.ReadKey();
 }
 }
}

var query = from a in groupA
   from b in groupB
   let sum = a + b
   where sum <12
   select new(a,b,sum);

where BoolenExpression1
where BoolenExpression2

var query = from s in students
      join c in courses on s.stId equals c.stId
      where c.courseName == "history"
　　　　　　　　　　　　　　 orderby s.stuName　　//排序
      select s.stuName; 

var query = from student in students
   group student by student.major;

   foreach (var s in query)
   {
    Console.WriteLine("{0}", s.key);
    foreach (var t in s)
    {
     console.writeLine(" {0}", t.Name);
    }
   }

var query = from s in students
      select s; //整个数据项

   var query = from s in students
      select s.stuName; //s中的一个字段

   var query = from a in groupA
      from b in groupB
      let sum = a + b
      where sum <12
      select new (a, b, sum);  //a，b，sum组成的新字段

var someInt = from a in groupA
    from b in groupB
    into groupAandB
    from c in groupAandB
    select c;

int[] num = { 2, 4, 6, 8, 10 };

 var numQuery = from number in num //查询语法
    where number <8
    select number;

 var numMethod = num.Where(x => x <8); //方法语法