Linq语法详细

闲言碎语

近期比较忙,但还是想写点什么,就分享一些基础的知识给大家看吧,希望能帮助一些linq新手,如果有其它疑问,可以进右上角群,进行交流探讨,谢谢。

开门见山

读这篇文章之前,我先说下,每一种搜索结果集,我都以三种方式变现出来,为啦更好的理解,希望不要嫌我啰嗦。

1.简单的linq语法

            //1
            var ss = from r in db.Am_recProScheme
                     select r;
            //2
            var ss1 = db.Am_recProScheme;
            //3
            string sssql = "select * from Am_recProScheme";

2.带where的查询

            //1
            var ss = from r in db.Am_recProScheme
                     where r.rpId > 10
                     select r;
            //2
            var ss1 = db.Am_recProScheme.Where(p => p.rpId > 10);
            //3
            string sssql = "select * from Am_recProScheme where rpid>10";

3.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";

4.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]";

5.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();

            //()linq to ef 好像不支持 Last() 
            var ss1 = db.Am_recProScheme.FirstOrDefault();
            //var ss1 = db.Am_recProScheme.First();          

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

6.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";

7.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";

8.包含,类似like '%%'

            //1
            var ss = from r in db.Am_recProScheme
                     where r.SortsText.Contains("张")
                     select r;
            //2
            var ss1 = db.Am_recProScheme.Where(p => p.SortsText.Contains("")).ToList();
            //3
            string sssql = "select * from Am_recProScheme where SortsText like '%张%'";

9.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";


//多字段

var result = (from item in data
group item by new { item.Name, item.Type } into items
select new
{
    items.Key.Name,
    items.Key.Type,
    Cnt = items.Count()
}).ToList();


var s = data.GroupBy(p => new { p.Type, p.Name }).Select(p=>new {
          p.Key.Type,
          p.Key.Name,
          cnt=p.Count()
}).ToList();


10.连接查询 

            //1
            var ss = from r in db.Am_recProScheme
                     join w in db.Am_Test_Result on r.rpId equals w.rsId
                     orderby r.rpId descending
                     select r;
            //2
            var ss1 = db.Am_recProScheme.Join(db.Am_Test_Result, p => p.rpId, r => r.rsId, (p, r) => p).OrderByDescending(p => p.rpId).ToList();
            //3
            string sssql = "select r.* from  [Am_recProScheme] as r inner join [dbo].[Am_Test_Result] as t on r.[rpId] = t.[rsId] order by r.[rpId] desc";

11.sql中的In

            //1
            var ss = from p in db.Am_recProScheme
                              where (new int?[] { 24, 25,26 }).Contains(p.rpId)
                              select p;
            foreach (var p in ss)
            {
                Response.Write(p.Sorts);
            }
            //2
            string st = "select * from Am_recProScheme where rpId in(24,25,26)";

 

如果你是linq新手,建议这十个常用的查询标记学习,再加上视图,基本上就能解决大部分的查询问题啦。

 

posted @ 2014-08-08 08:27  张龙豪  阅读(...)  评论(...编辑  收藏