asp.net Linq 实现分组查询

首先我们还是先建立一个person.cs类

public class person
{
　　public string name
　　{ get; set; }
　　public int age
　　{ get; set; }
　　public string sex
　　{ get; set; }
}

接下来我们往这个person类添加数据：

List plist1 = new List();
　　plist1.Add(new person { name = "cxx1", age = 24, sex = "男" });
　　plist1.Add(new person { name = "www.baidu.com", age = 25, sex = "男" });
　　plist1.Add(new person { name = "www.52mvc.com", age = 26, sex = "男" });
　　List plist2 = new List();
　　plist2.Add(new person { name = "cxx1", age = 24, sex = "男" });
　　plist2.Add(new person { name = "cxx2", age = 28, sex = "男" });
　　plist2.Add(new person { name = "cxx4", age = 27, sex = "男" });
　　plist2.Add(new person { name = "cxx5", age = 28, sex = "男" });
　　// asp.net
　　var query = from person p in plist1
　　join person per in plist2
　　on p.name equals per.name
　　select new
　　{
　　名称=p.name,
　　性别=p.sex,
　　年龄=p.age
　　};
　　gd2.DataSource = query;
　　gd2.DataBind();

返回的结果是：

　　备注：这个方法是要查找出 plist1 与 plist2 之中，name名称有相同记录的数据。
　　

接下来我们来看看sql中的左连接left join 在linq中如何实现
　　还是先来创建两个cs 类。

///
/// 手机列表
///
public class MobileStore
{
　　public string mobId
　　{ set; get; }
　　public string mobName
　　{ set; get; }
}

/// 手机销售表
　　///
　　public class MobileSale
　　{
　　public string Sid
　　{ set; get; }
　　public string mobId
　　{ set; get; }
　　public string mobName
　　{ set; get; }
　　public string price
　　{ set; get; }
　　}
　　List listStore = new List();
　　listStore.Add(new MobileStore { mobId = "1", mobName = "N86" });
　　listStore.Add(new MobileStore { mobId = "2", mobName = "N82" });
　　listStore.Add(new MobileStore { mobId = "3", mobName = "N81" });
　　listStore.Add(new MobileStore { mobId = "4", mobName = "N95" });
　　listStore.Add(new MobileStore { mobId = "5", mobName = "N85" });
　　listStore.Add(new MobileStore { mobId = "6", mobName = "N97" });
　　List listSale = new List();
　　listSale.Add(new MobileSale { Sid="1" ,mobId="1",mobName="N86",price="100"});
　　listSale.Add(new MobileSale { Sid="2", mobId = "2", mobName = "N82",price="220" });
　　listSale.Add(new MobileSale { Sid = "3", mobId = "3", mobName = "N81", price = "300" });
　　var query = from MobileStore m in listStore
　　join MobileSale sale in listSale
　　on m.mobId equals sale.mobId into joinm
　　from j in joinm.DefaultIfEmpty()
　　select new
　　{
　　ID = m.mobId,
　　名称 = m.mobName,
　　价格 = j == null ? "暂无数据" : j.price,
　　};
　　gd.DataSource = query;
　　gd.DataBind();