Linq语法详细

转&＃xff1a;https://www.cnblogs.com/knowledgesea/p/3897665.html

闲言碎语

近期比较忙&＃xff0c;但还是想写点什么&＃xff0c;就分享一些基础的知识给大家看吧&＃xff0c;希望能帮助一些linq新手&＃xff0c;如果有其它疑问&＃xff0c;可以进右上角群&＃xff0c;进行交流探讨&＃xff0c;谢谢。

开门见山

读这篇文章之前&＃xff0c;我先说下&＃xff0c;每一种搜索结果集&＃xff0c;我都以三种方式变现出来&＃xff0c;为啦更好的理解&＃xff0c;希望不要嫌我啰嗦。

1.简单的linq语法

//1var ss &＃61; from r in db.Am_recProSchemeselect r;//2var ss1 &＃61; db.Am_recProScheme;//3string sssql &＃61; "select * from Am_recProScheme";

2.带where的查询

//1var ss &＃61; from r in db.Am_recProSchemewhere r.rpId > 10select r;//2var ss1 &＃61; db.Am_recProScheme.Where(p &＃61;> p.rpId > 10);//3string sssql &＃61; "select * from Am_recProScheme where rpid>10";

3.简单的函数计算&＃xff08;count&＃xff0c;min&＃xff0c;max&＃xff0c;sum&＃xff09;

//1获取最大的rpId//var ss &＃61; (from r in db.Am_recProScheme// select r).Max(p &＃61;> p.rpId);获取最小的rpId//var ss &＃61; (from r in db.Am_recProScheme// select r).Min(p &＃61;> p.rpId);//获取结果集的总数//var ss &＃61; (from r in db.Am_recProScheme // select r).Count();//获取rpId的和var ss &＃61; (from r in db.Am_recProSchemeselect r).Sum(p &＃61;> p.rpId);//2//var ss1 &＃61; db.Am_recProScheme.Max(p&＃61;>p.rpId);//var ss1 &＃61; db.Am_recProScheme.Min(p &＃61;> p.rpId);//var ss1 &＃61; db.Am_recProScheme.Count() ;var ss1 &＃61; db.Am_recProScheme.Sum(p &＃61;> p.rpId);Response.Write(ss);//3string sssql &＃61; "select max(rpId) from Am_recProScheme";sssql &＃61; "select min(rpId) from Am_recProScheme";sssql &＃61; "select count(1) from Am_recProScheme";sssql &＃61; "select sum(rpId) from Am_recProScheme";

4.排序order by desc/asc

var ss &＃61; from r in db.Am_recProSchemewhere r.rpId > 10orderby r.rpId descending //倒序// orderby r.rpId ascending //正序select r;//正序var ss1 &＃61; db.Am_recProScheme.OrderBy(p &＃61;> p.rpId).Where(p &＃61;> p.rpId > 10).ToList();//倒序var ss2 &＃61; db.Am_recProScheme.OrderByDescending(p &＃61;> p.rpId).Where(p &＃61;> p.rpId > 10).ToList();string sssql &＃61; "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 &＃61; (from r in db.Am_recProScheme select r).FirstOrDefault();//&＃xff08;&＃xff09;linq to ef 好像不支持 Last() var ss1 &＃61; db.Am_recProScheme.FirstOrDefault();//var ss1 &＃61; db.Am_recProScheme.First(); string sssql &＃61; "select top(1) * from Am_recProScheme";

6.跳过前面多少条数据取余下的数据

//1var ss &＃61; (from r in db.Am_recProSchemeorderby r.rpId descendingselect r).Skip(10); //跳过前10条数据&＃xff0c;取10条之后的所有数据 //2 var ss1 &＃61; db.Am_recProScheme.OrderByDescending(p &＃61;> p.rpId).Skip(10).ToList();//3string sssql &＃61; "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

//1var ss &＃61; (from r in db.Am_recProSchemewhere r.rpId > 10orderby r.rpId descendingselect 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&＃xff0c;获取指定数量&＃xff08;10&＃xff09;的连续数据var ss1 &＃61; db.Am_recProScheme.OrderByDescending(p &＃61;> p.rpId).Where(p &＃61;> p.rpId > 10).Skip(10).Take(10).ToList();//3string sssql &＃61; "select * from (select ROW_NUMBER()over(order by rpId desc) as rowNum, * from [Am_recProScheme]) as t where rowNum>10 and rowNum<&＃61;20";

8.包含&＃xff0c;类似like &＃39;%%&＃39;

//1var ss &＃61; from r in db.Am_recProSchemewhere r.SortsText.Contains("张")select r;//2var ss1 &＃61; db.Am_recProScheme.Where(p &＃61;> p.SortsText.Contains("张")).ToList();//3string sssql &＃61; "select * from Am_recProScheme where SortsText like &＃39;%张%&＃39;";

9.分组group by

//1var ss &＃61; from r in db.Am_recProSchemeorderby r.rpId descendinggroup r by r.recType into nselect new{n.Key, //这个Key是recTyperpId &＃61; n.Sum(r &＃61;> r.rpId), //组内rpId之和MaxRpId &＃61; n.Max(r &＃61;> r.rpId),//组内最大rpIdMinRpId &＃61; n.Min(r &＃61;> r.rpId), //组内最小rpId};foreach (var t in ss){Response.Write(t.Key &＃43; "--" &＃43; t.rpId &＃43; "--" &＃43; t.MaxRpId &＃43; "--" &＃43; t.MinRpId);}//2var ss1 &＃61; from r in db.Am_recProSchemeorderby r.rpId descendinggroup r by r.recType into nselect n;foreach (var t in ss1){Response.Write(t.Key &＃43; "--" &＃43; t.Min(p &＃61;> p.rpId));}//3var ss2 &＃61; db.Am_recProScheme.GroupBy(p &＃61;> p.recType);foreach (var t in ss2){Response.Write(t.Key &＃43; "--" &＃43; t.Min(p &＃61;> p.rpId));}//4string sssql &＃61; "select recType,min(rpId),max(rpId),sum(rpId) from Am_recProScheme group by recType";

10.连接查询 

//1var ss &＃61; from r in db.Am_recProSchemejoin w in db.Am_Test_Result on r.rpId equals w.rsIdorderby r.rpId descendingselect r;//2var ss1 &＃61; db.Am_recProScheme.Join(db.Am_Test_Result, p &＃61;> p.rpId, r &＃61;> r.rsId, (p, r) &＃61;> p).OrderByDescending(p &＃61;> p.rpId).ToList();//3string sssql &＃61; "select r.* from [Am_recProScheme] as r inner join [dbo].[Am_Test_Result] as t on r.[rpId] &＃61; t.[rsId] order by r.[rpId] desc";

11.sql中的In

按 Ctrl&＃43;C

按 Ctrl&＃43;C