C# LINQ语法详解
作者:互联网
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";
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)";
实例用法:
//数据库 + 自定义名称 =new 数据库 mydbDataContext con = new mydbDataContext(); //模糊查询表达式中用.Contains con.car.Where(r=>r.name.Contains(TextBox1.Text.Trim())).ToList(); //开头查用.StartWith con.car.Where(r => r.name.StartsWith(TextBox1.Text)).ToList(); //结尾查用.EndWith con.car.Where(r => r.name.EndsWith(TextBox1.Text)).ToList(); //最大值 con.car.Max(r => r.price * r.oil).ToString(); //最小值 con.car.Min(r => r.price).ToString(); //求和 con.car.Sum(r => r.price).ToString(); //平均值 con.car.Average(r => r.price).ToString(); //升序: con.car.OrderBy(r => r.price).ToList(); //降序: con.car.OrderByDescending(r => r.price).ToList(); //上一页,下一页,组合查询: int PageCount = 5;//每页显示条数 //上一页,PageCount_Label.Text为当前页码 int pageNum = Convert.ToInt32(PageCount_Label.Text) - 1; Repeater1.DataSource = con.car.Skip((pageNum - 1) * PageCount).Take(PageCount); Repeater1.DataBind(); PageCount_Label.Text = pageNum.ToString(); //下一页 int pageNum = Convert.ToInt32(PageCount_Label.Text) + 1; Repeater1.DataSource = con.car.Skip((pageNum - 1) * PageCount).Take(PageCount); Repeater1.DataBind(); PageCount_Label.Text = pageNum.ToString(); //组合查询的点击事件 List<car> list = con.car.ToList(); if (TextBox2.Text != "") { List<car> list1 = con.car.Where(r => r.name.Contains(TextBox2.Text)).ToList(); list = list.Intersect(list1).ToList(); } if (TextBox3.Text != "") { List<car> list1 = con.car.Where(r => r.oil == Convert.ToDecimal(TextBox3.Text)).ToList(); list = list.Intersect(list1).ToList(); } if (TextBox4.Text != "") { List<car> list1 = con.car.Where(r => r.powers == Convert.ToInt32(TextBox4.Text)).ToList(); list = list.Intersect(list1).ToList(); } Repeater1.DataSource = list; Repeater1.DataBind();
标签:C#,db,recProScheme,Am,LINQ,rpId,详解,var,select 来源: https://www.cnblogs.com/zhaoshujie/p/10434657.html