型別 查詢變數= from 臨時變數 in 集合物件或資料庫物件

            [where 條件表示式]
            [order by 條件]
            select 臨時變數中被查詢的值
            [group by 條件]

            linq的分類：linq to objects,linq to datasets,linq to sql,linq to entities,linq to XML

下面是程式碼練習：

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

namespace _71_linq交叉連線
{
    class Program
    {
        static void Main(string[] args)
        {
            //宣告兩個CHAR型別的資料來源
            char[] upperCase = { 'A', 'B', 'C' };
            char[] lowerCase = { 'x', 'y', 'z' };

            var joinQuery1 =
                from upper in upperCase 
                from lower in lowerCase
                select new { upper, lower };

            var joinQuery2 =
                from lower in lowerCase
                from upper in upperCase
                select new { upper, lower };

            foreach (var pair in joinQuery1)
            {
                Console.WriteLine(string.Format("{0}匹配{1}", pair.upper, pair.lower));
            }

            foreach (var pair in joinQuery2)
            {
                Console.WriteLine(string.Format("{0}匹配{1}", pair.lower, pair.upper));
            }

            Console.ReadKey();

        }
    }
}