时间： 2016/10/30 13:04:07
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，可以加我QQ，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 //1
2 var ss = from r in db.Am_recProScheme
3 select r;
4 //2
5 var ss1 = db.Am_recProScheme;
6 //3
7 string sssql = "select * from Am_recProScheme";
1 //1
2 var ss = from r in db.Am_recProScheme
3 where r.rpId > 10
4 select r;
5 //2
6 var ss1 = db.Am_recProScheme.Where(p => p.rpId > 10);
7 //3
8 string sssql = "select * from Am_recProScheme where rpid>10";
3.简单的函数计算（count，min，max，sum）
1 //1
2 ////获取最大的rpId
3 //var ss = (from r in db.Am_recProScheme
4 // select r).Max(p => p.rpId);
5 ////获取最小的rpId
6 //var ss = (from r in db.Am_recProScheme
7 // select r).Min(p => p.rpId);
8 //获取结果集的总数
9 //var ss = (from r in db.Am_recProScheme
10 // select r).Count();
11 //获取rpId的和
12 var ss = (from r in db.Am_recProScheme
13 select r).Sum(p => p.rpId);
14
15
16 //2
17 //var ss1 = db.Am_recProScheme.Max(p=>p.rpId);
18 //var ss1 = db.Am_recProScheme.Min(p => p.rpId);
19 //var ss1 = db.Am_recProScheme.Count() ;
20 var ss1 = db.Am_recProScheme.Sum(p => p.rpId);
21 Response.Write(ss);
22
23 //3
24 string sssql = "select max(rpId) from Am_recProScheme";
25 sssql = "select min(rpId) from Am_recProScheme";
26 sssql = "select count(1) from Am_recProScheme";
27 sssql = "select sum(rpId) from Am_recProScheme";
4.排序order by desc/asc
1 var ss = from r in db.Am_recProScheme
2 where r.rpId > 10
3 orderby r.rpId descending //倒序
4 // orderby r.rpId ascending //正序
5 select r;
6
7 //正序
8 var ss1 = db.Am_recProScheme.OrderBy(p => p.rpId).Where(p => p.rpId > 10).ToList();
9 //倒序
10 var ss2 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).ToList();
11
12 string sssql = "select * from Am_recProScheme where rpid>10 order by rpId [desc|asc]";
5.top(1)
1 //如果取最后一个可以按倒叙排列再取值
2 var ss = (from r in db.Am_recProScheme
3 select r).FirstOrDefault();
4
5 //（）linq to ef 好像不支持 Last()
6 var ss1 = db.Am_recProScheme.FirstOrDefault();
7 //var ss1 = db.Am_recProScheme.First();
8
9 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 //1
2 var ss = (from r in db.Am_recProScheme
3 orderby r.rpId descending
4 select r).Skip(10); //跳过前10条数据，取10条之后的所有数据
5 //2
6 var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Skip(10).ToList();
7 //3
8 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 //1
2 var ss = (from r in db.Am_recProScheme
3 where r.rpId > 10
4 orderby r.rpId descending
5 select r).Skip(10).Take(10); //取第11条到第20条数据
6
7 //2 Take(10): 数据从开始获取，获取指定数量（10）的连续数据
8 var ss1 = db.Am_recProScheme.OrderByDescending(p => p.rpId).Where(p => p.rpId > 10).Skip(10).Take(10).ToList();
9 //3
10 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 //1
2 var ss = from r in db.Am_recProScheme
3 where r.SortsText.Contains("张")
4 select r;
5 //2
6 var ss1 = db.Am_recProScheme.Where(p => p.SortsText.Contains("张")).ToList();
7 //3
8 string sssql = "select * from Am_recProScheme where SortsText like ''%张%''";
9.分组group by
1 //1
2 var ss = from r in db.Am_recProScheme
3 orderby r.rpId descending
4 group r by r.recType into n
5 select new
6 {
7 n.Key, //这个Key是recType
8 rpId = n.Sum(r => r.rpId), //组内rpId之和
9 MaxRpId = n.Max(r => r.rpId),//组内最大rpId
10 MinRpId = n.Min(r => r.rpId), //组内最小rpId
11 };
12 foreach (var t in ss)
13 {
14 Response.Write(t.Key + "--" + t.rpId + "--" + t.MaxRpId + "--" + t.MinRpId);
15 }
16 //2
17 var ss1 = from r in db.Am_recProScheme
18 orderby r.rpId descending
19 group r by r.recType into n
20 select n;
21 foreach (var t in ss1)
22 {
23 Response.Write(t.Key + "--" + t.Min(p => p.rpId));
24 }
25 //3
26 var ss2 = db.Am_recProScheme.GroupBy(p => p.recType);
27 foreach (var t in ss2)
28 {
29 Response.Write(t.Key + "--" + t.Min(p => p.rpId));
30 }
31 //4
32 string sssql = "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";
1 //1
2 var ss = from r in db.Am_recProScheme
3 join w in db.Am_Test_Result on r.rpId equals w.rsId
4 orderby r.rpId descending
5 select r;
6 //2
7 var ss1 = db.Am_recProScheme.Join(db.Am_Test_Result, p => p.rpId, r => r.rsId, (p, r) => p).OrderByDescending(p => p.rpId).ToList();
8 //3
9 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";
1 //1
2 var ss = from p in db.Am_recProScheme
3 where (new int?[] { 24, 25,26 }).Contains(p.rpId)
4 select p;
5 foreach (var p in ss)
6 {
7 Response.Write(p.Sorts);
8 }
9 //2
10 string st = "select * from Am_recProScheme where rpId in(24,25,26)";
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