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左连接日常使用比较多，假如有两张表tbRoom和tbUserInfo。

得到房间住户信息：

C＃var list = from r in tbRooms                          join ui in tbUserInfos                          on r.UserName equals ui.UserName into userrooms                          from ur in userrooms.DefaultIfEmpty()                          select new                           {
                                  FirstName = (ur.FirstName ==null ? "N/A": ur.FirstName),                               LastName = (ur.LastName == null ? "N/A":ur.LastName),                               RoomName = r.Name                           };                           VB:Dim list = from r in tbRooms     Group join ui in tbUserInfos      on  r.UserName equals ui.UserName into userrooms                          from ur in userrooms.DefaultIfEmpty()                          select                                  FirstName = if(ur.FirstName = nothing, "N/A", ur.FirstName),                               LastName = if(ur.LastName = nothing,  "N/A",ur.LastName),                               RoomName = r.Name

另一个多表左联接的例子：

**ＳＱＬ：**SELECT id, name, jname, cname           FROM userinfo u           LEFT JOIN job j on u.job = j.jid           LEFT JOIN city c on u.city = c.cid         **Ｃ＃　Linq:**var list = (      from u in dc.userinfos          join j in dc.jobs on u.job equals j.jid into j_join      from x in j_join.DefaultIfEmpty()          join c in dc.cities on u.city equals c.cid into c_join      from v in c_join.DefaultIfEmpty()      select new      {
             id = u.id,          name = u.name,          jname = x.jname,          cname = v.cname,          /*u1=u,x1=x,v1=v*/          //不要用对象的方式 因为对象可能为null那么对象.属性就会抛异常      }      ).ToList();            for (var i = 0; i < list.Count(); i++)      {
             Console.WriteLine(list[i].name + '\t' + list[i].jname + '\t' + list[i].cname); //字段为null不报异常          //Console.WriteLine(list[i].u1.name+'\t'+list[i].x1.jname+'\t'+list[i].v1.cname+"\r\n"); //对象x1 v1 有可能为null 抛异常      }      Console.ReadLine();

VB.NET

**ＳＱＬ：**SELECT id, name, jname, cname           FROM userinfo u           LEFT JOIN job j on u.job = j.jid           LEFT JOIN city c on u.city = c.cid         **VB　Linq:**Dim list = (      from u in dc.userinfos          join j in dc.jobs on u.job equals j.jid Into  j_join = Group     from x in j_join.DefaultIfEmpty()          join c in dc.cities on u.city equals c.cid Into c_join  = Group    from v in c_join.DefaultIfEmpty()      select new  with    {          .id = u.id,          .name = u.name,          .jname = x.jname,          .cname = v.cname      }      ).ToList();

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