c#Linq联合查询

        public void Test2()
        {
            var queryResult1 = from e in empArray
                              from l in empLevelArray
                              select new { e, l };

            var queryResult2 = from e in empArray
                              from l in empLevelArray
                              where e.LevelNum == l.LevelNum
                              select new { e, l };

            var queryResult3 = from e in empArray
                              from l in empLevelArray
                              orderby e.LevelNum,e.Name                    #进行排序，按照等级和姓名
                              where e.LevelNum == l.LevelNum
                              select new { e.Name, l.LevelName, l.Salary };
                             
            foreach (var item in queryResult1)
            {
                Console.WriteLine(item);
            }
        }

查询两个表中相似的部分，或者取各自的一部分。

联合查询同样会遇到排序和其他的表现形式：

        /// <summary>
        /// 学习Join On 关键字
        /// </summary>
        public void Test4()
        {
            var queryResult = from e in empArray
                              join l in empLevelArray
                              on e.LevelNum equals l.LevelNum         //连接条件
                              where e.LevelNum > 1 && l.Salary > 10000
                              select new { e.LevelNum, l.Salary };
            foreach (var item in queryResult)
            {
                Console.WriteLine(item);
            }
        }

        /// <summary>
        /// 学习gruop by 分组
        /// </summary>
        public void Test5()
        {
            var queryResult = from e in empArray
                              group e by e.LevelNum into g
                              select new { g.Key, counts = g.Count() };
            foreach (var item in queryResult)
            {
                Console.WriteLine("级别："+item.Key+"  个数："+item.counts);
            }
        }