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Linq常用语法(2)

关键词:Linq语法Linq  阅读(1255) 赞(17)

[摘要]本文是对Linq语法详细的讲解,对学习C#编程技术有所帮助,与大家分享。

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("张")).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";

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。

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