Linq 语法举例

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)";