join子句使用equals关键字进行相等比较，而不是常用的双等号。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace LINQ_join
{
class Program
{
static void Main(string[] args)
{
//定义两个数据源
List<GustInfo> gList = new List<GustInfo>()
{
new GustInfo(){ Name="DebugLZQ",Age=26,Tel="187********"},
new GustInfo(){ Name="Sarah",Age=25,Tel="159********"},
new GustInfo(){ Name="Jerry",Age=35,Tel="135********"},
new GustInfo(){ Name="M&M",Age=16,Tel="136********"},
new GustInfo(){ Name="DebugMan",Age=26,Tel="136********"},
new GustInfo(){ Name="Jerry&Tom",Age=19,Tel="136********"},
};
List<GuestTitle> titleList = new List<GuestTitle>()
{
new GuestTitle(){Name="DebugLZQ",Title="Soft Engineer"},
new GuestTitle(){Name="DebugLZQ",Title="Team Leader"},
new GuestTitle(){Name="Sarah",Title="Test Engineer"},
new GuestTitle(){Name="Jerry",Title="Head Master"}
};
//1.根据姓名进行内连接
var query = from guest in gList
join title in titleList on guest.Name equals title.Name
select new { Name=guest.Name ,Title=title.Title,Age=guest.Age };
foreach (var g in query)
{
Console.WriteLine("{0} {1} 年龄：{2}",g.Name,g.Title ,g.Age );
}
Console.ReadKey(false);
//前面的多个from实现相同的作用:与内连接区别在于：这个中间的操作是叉乘获得笛卡尔积
var query2=from guest in gList
from title in titleList
where guest.Name==title.Name
select new { Name = guest.Name, foreach (var g in query2)
{
Console.WriteLine("{0} {1} 年龄：{2}", g.Name, g.Title, g.Age);
}
Console.ReadKey(false);
//2.根据姓名进行分组连接
//根据名字分组后，得到每个名字下的全部名称
var query3 = from guest in gList
join title in titleList on guest.Name equals title.Name into tgroup
select new { Name=guest.Name,Titles=tgroup };
foreach (var g in query3)
{
Console.WriteLine(g.Name);
foreach (var g2 in g.Titles)
{
Console.WriteLine(" {0}",g2.Title );
}
}
Console.ReadKey(false);
//3.根据姓名进行左外连接
//无职务的输出为空缺
var query4 = from guest in gList
join title in titleList on guest.Name equals title.Name into tgroup
from subtitle in tgroup.DefaultIfEmpty()
select new { Name=guest.Name,Title=subtitle==null?"空缺":subtitle.Title };
foreach (var g in query4)
{
Console.WriteLine("{0} {1} ",g.Name ,g.Title );
}
Console.ReadKey(false);
}
}
}
