经典Linq实例语句
从技术角度而言,LINQ定义了大约40个查询操作符,如select、from、in、where以及order by(C#中)。使用这些操作符可以编写查询语句。不过,这些查询还可以基于很多类型的数据,每个数据类型都需要一个单独的LINQ类型。
1、简单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)";
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