• 简单的linq语法


    1.简单的linq语法

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

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                //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";
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    3.简单的函数计算(count,min,max,sum)

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                //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";
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    4.排序order by desc/asc

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                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]";
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    5.top(1)

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                //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";
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    6.跳过前面多少条数据取余下的数据

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                //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";
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    7.分页数据查询

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                //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";
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    8.包含,类似like '%%'

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                //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%'";
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    9.分组group by

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                //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";
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    10.连接查询 

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                //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";
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    11.sql中的In

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                //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)";
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  • 原文地址:https://www.cnblogs.com/ddzzhh/p/7596820.html
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