Linq语法详细

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("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";