代码：

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data;using System.Reflection;namespace TestConsole{    public class Program    {        public static void Main(string[] args)        {            var classify_list = new List
     
                  {                new Alliance_FAQ_Classify{ClassifyID =1,ClassifyName ="酒店"},                new Alliance_FAQ_Classify{ClassifyID =2,ClassifyName ="机票"},                new Alliance_FAQ_Classify{ClassifyID =3,ClassifyName ="团购"},                new Alliance_FAQ_Classify{ClassifyID =5,ClassifyName ="旅游"},                new Alliance_FAQ_Classify{ClassifyID =8,ClassifyName ="Other"}            };            var info_list = new List
      
                   {                new Alliance_FAQ_Info{FAQID =1,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =2,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =3,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =4,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =5,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =6,ClassifyID =1},                new Alliance_FAQ_Info{FAQID =7,ClassifyID =2},                new Alliance_FAQ_Info{FAQID =8,ClassifyID =2},                new Alliance_FAQ_Info{FAQID =9,ClassifyID =2},                new Alliance_FAQ_Info{FAQID =10,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =11,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =12,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =13,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =14,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =15,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =16,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =17,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =18,ClassifyID =3},                new Alliance_FAQ_Info{FAQID =19,ClassifyID =5},                new Alliance_FAQ_Info{FAQID =22,ClassifyID =5}            };            var info_group = from a in info_list                             group a by a.ClassifyID into g                             select new                             {                                 ClassifyID=g.Key,                                 TotalCount=g.Count()                             };            foreach (var g in info_group)            {                Console.WriteLine("ClassifyID:" + g.ClassifyID + "     TotalCount:" + g.TotalCount);            }            Console.WriteLine("=================================================");            Console.WriteLine("Left Join:");            var left_list = from a in info_group                       join b in classify_list                       on a.ClassifyID equals b.ClassifyID into joinData                       from c in joinData.DefaultIfEmpty()                       select new                       {                           c.ClassifyID,                           Count = a != null ? a.TotalCount : 0,                           c.ClassifyName                       };            foreach (var l in left_list)            {                Console.WriteLine("ClassifyID:" + l.ClassifyID + "     Count:" + l.Count + "     ClassifyName:" + l.ClassifyName);            }            Console.WriteLine("=================================================");            Console.WriteLine("Right Join:");            var right_list = from a in classify_list                       join b in info_group                       on a.ClassifyID equals b.ClassifyID into joinData                       from c in joinData.DefaultIfEmpty()                       select new                       {                           a.ClassifyID,                           Count = c != null ? c.TotalCount : 0,                           a.ClassifyName                        };            foreach (var r in right_list)            {                Console.WriteLine("ClassifyID:" + r.ClassifyID + "     Count:" + r.Count + "     ClassifyName:" + r.ClassifyName);            }            Console.ReadLine();        }    }    public class Alliance_FAQ_Info    {        public int FAQID { get; set; }        public int ClassifyID { get; set; }    }    public class Alliance_FAQ_Classify    {        public int ClassifyID { get; set; }        public string ClassifyName { get; set; }    }}
      
     

 可以发现第一个就是满表

http://www.cnblogs.com/redmondfan/archive/2013/08/23/3276811.html

http://www.cnblogs.com/shenqiboy/p/3260105.html

 

DataTable dtA = new DataTable();            dtA.Columns.Add("id", typeof(int));            dtA.Columns.Add("price", typeof(string));            dtA.Rows.Add(1, "100");            dtA.Rows.Add(2, "100");            DataTable dtB = dtA.Clone();            dtB.Rows.Add(1, "100");            dtB.Rows.Add(3, "100");            DataTable dtC = dtA.Clone();            dtC.Columns.Add("price_excel");            var leftData = from a in dtA.AsEnumerable()                           join b in dtB.AsEnumerable()                           on a.Field
     
      ("id") equals b.Field
      
       ("id") into g                           from b in g.DefaultIfEmpty()                           select new                           {                               id = a.Field
       
        ("id"),                               price = a.Field
        
         ("price"),                               price_excel = b == null ? "Null" : b.Field
         
          ("price")                           };            var rightData = from b in dtB.AsEnumerable()                            where !dtA.AsEnumerable().Select(a => a.Field
          
           ("id")).Contains(b.Field
           
            ("id")) select new { id = b.Field
            
             ("id"), price = "Null", price_excel = b.Field
             
              ("price") }; var fullJoinData = leftData.Union(rightData); fullJoinData.ToList().ForEach(q => dtC.Rows.Add(q.id, q.price, q.price_excel)); for(var i=0;i
             
            
           
          
         
        
       
      
     

 full join

http://blog.csdn.net/q107770540/article/details/7282005