Linq与lamda写法对比

最新推荐文章于 2024-09-08 19:51:38 发布

whaxrl

最新推荐文章于 2024-09-08 19:51:38 发布

阅读量567

点赞数

CC 4.0 BY-SA版权

分类专栏： asp.net 文章标签： Linq lamda asp.net

本文链接：https://blog.youkuaiyun.com/whaxrl/article/details/49760171

asp.net 专栏收录该内容

94 篇文章

订阅专栏

本文探讨了Linq与Lambda表达式在数据处理中的应用，包括简单的函数计算如count、min、max和sum，排序order by及其desc/asc方向，使用top获取顶部记录，跳过指定数量的数据取剩余部分，以及实现分页查询和数据分组。通过实例展示了两种方式的异同和应用场景。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

1、简单的函数计算（count，min，max，sum）

            //1
            /**/////获取最大的rpId
            var ss = (from r in db.Am_recProScheme
                      select r).Max(p => p.rpId);
            /**/////获取最小的rpId
            var ss = (from r in db.Am_recProScheme
                      select r).Min(p => p.rpId);
            //获取结果集的总数
              var ss = (from r in db.Am_recProScheme                  
                     select r).Count();
            //获取rpId的和
            var ss = (from r in db.Am_recProScheme
                      select r).Sum(p => p.rpId);


            //2
            var ss1 = db.Am_recProScheme.Max(p=>p.rpId);
            var ss1 = db.Am_recProScheme.Min(p => p.rpId);
            var ss1 = db.Am_recProScheme.Count() ;
            var ss1 = db.Am_recProScheme.Sum(p => p.rpId);
            Response.Write(ss);

            //3
            string sssql = "select max(rpId) from Am_recProScheme";
            sssql = "select min(rpId) from Am_recProScheme";
            sssql = "select count(1) from Am_recProScheme";
            sssql = "select sum(rpId) from Am_recProScheme";

2、排序order by desc/asc

          var ss = from r in db.Am_recProScheme
                     where r.rpId > 10
                     orderby r.rpId descending  //倒序
                     //  orderby r.rpId ascending   //正序
                     select r;

          //正序
           var ss1 = db.Am_recProScheme.OrderBy(p => p.rpId).Where(p => p.rpId > 10).ToList();

          //倒序
           var ss2 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).ToList();

          string sssql = "select * from Am_recProScheme where rpid>10 order by rpId [desc|asc]";

3、top

          //1
          //如果取最后一个可以按倒叙排列再取值
           var ss = (from r in db.Am_recProScheme select r).FirstOrDefault();

          //2
          string sssql = "select top(1) * from Am_recProScheme";

4、跳过前面多少条数据取余下的数据

             //1
           var ss = (from r in db.Am_recProScheme
                      orderby r.rpId descending
                      select r).Skip(10); //跳过前10条数据，取10条之后的所有数据 
  
             //2  
           var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();

           //3
           string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10";

5、分页数据查询

             //1
           var ss = (from r in db.Am_recProScheme
                      where r.rpId > 10
                      orderby r.rpId descending
                      select r).Skip(10).Take(10); //取第11条到第20条数据                   

            //2 Take(10): 数据从开始获取，获取指定数量（10）的连续数据
            var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();

           //3
           string sssql = "select * from  (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10 and rowNum<=20";

6、分组group by

              //1
            var ss = from r in db.Am_recProScheme
                     orderby r.rpId descending
                     group r by r.recType into n
                     select new
                     {
                         n.Key,  //这个Key是recType
                         rpId = n.Sum(r => r.rpId), //组内rpId之和
                         MaxRpId = n.Max(r => r.rpId),//组内最大rpId
                         MinRpId = n.Min(r => r.rpId), //组内最小rpId
                     };
            foreach (var t in ss)
            {
                Response.Write(t.Key + "--" + t.rpId + "--" + t.MaxRpId + "--" + t.MinRpId);
            }

            //2
            var ss1 = from r in db.Am_recProScheme
                     orderby r.rpId descending
                     group r by r.recType into n
                     select n;
            foreach (var t in ss1)
            {
                Response.Write(t.Key + "--" + t.Min(p => p.rpId));
            }

            //3
            var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);
            foreach (var t in ss2)
            {
                Response.Write(t.Key + "--" + t.Min(p => p.rpId));
            }

            //4
            string sssql = "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";

参考资料： Linq与lamda的对比 http://www.studyofnet.com/news/1095.html