# 开门见山

## 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";           //多字段

var result = (from item in data
group item by new { item.Name, item.Type } into items
select new
{
items.Key.Name,
items.Key.Type,
Cnt = items.Count()
}).ToList();

var s = data.GroupBy(p => new { p.Type, p.Name }).Select(p=>new {
p.Key.Type,
p.Key.Name,
cnt=p.Count()
}).ToList();



## 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)";

# 如果你是linq新手，建议这十个常用的查询标记学习，再加上视图，基本上就能解决大部分的查询问题啦。

posted @ 2014-08-08 08:27  张龙豪  阅读(...)  评论(...编辑  收藏