Linq101-Join
using System;
using System.Collections.Generic;
using System.Linq; namespace Linq101
{
internal class Join
{
/// <summary>
/// This sample shows how to efficiently join elements of two sequences based on equality between key expressions over the two.
/// </summary>
public void Linq102()
{
string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
List<Data.Product> products = Data.GetProductList(); var q = from c in categories
join p in products on c equals p.Category
select new { Category = c, p.ProductName }; ObjectDumper.Write(q);
} /// <summary>
/// Using a group join you can get all the products that match a given category bundled as a sequence.
/// </summary>
public void Linq103()
{
string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
List<Data.Product> products = Data.GetProductList(); var q = from c in categories
join p in products on c equals p.Category into ps
select new { Category = c, Products = ps }; foreach (var v in q)
{
Console.WriteLine(v.Category + ":");
foreach (var p in v.Products)
{
Console.WriteLine(" " + p.ProductName);
}
}
} /// <summary>
/// The group join operator is more general than join, as this slightly more verbose version of the cross join sample shows.
/// </summary>
public void Linq104()
{
string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
List<Data.Product> products = Data.GetProductList(); var q = from c in categories
join p in products on c equals p.Category into ps
from p in ps
select new { Category = c, p.ProductName }; foreach (var v in q)
{
Console.WriteLine(v.ProductName + ": " + v.Category);
}
} /// <summary>
/// A so-called outer join can be expressed with a group join. A left outer joinis like a cross join,
/// except that all the left hand side elements get included at least once, even if they don't match any right hand side elements.
/// Note how Vegetablesshows up in the output even though it has no matching products.
/// </summary>
public void Linq105()
{
string[] categories = { "Beverages", "Condiments", "Vegetables", "Dairy Products", "Seafood" };
List<Data.Product> products = Data.GetProductList(); var q = from c in categories
join p in products on c equals p.Category into ps
from p in ps.DefaultIfEmpty()
select new { Category = c, ProductName = p == null ? "(No Products)" : p.ProductName }; foreach (var v in q)
{
Console.WriteLine(v.ProductName + ": " + v.Category);
}
}
}
}
Linq101-Join的更多相关文章
- SQL Server-聚焦IN VS EXISTS VS JOIN性能分析(十九)
前言 本节我们开始讲讲这一系列性能比较的终极篇IN VS EXISTS VS JOIN的性能分析,前面系列有人一直在说场景不够,这里我们结合查询索引列.非索引列.查询小表.查询大表来综合分析,简短的内 ...
- SQL Server-聚焦NOT IN VS NOT EXISTS VS LEFT JOIN...IS NULL性能分析(十八)
前言 本节我们来综合比较NOT IN VS NOT EXISTS VS LEFT JOIN...IS NULL的性能,简短的内容,深入的理解,Always to review the basics. ...
- Nested Loops join时显示no join predicate原因分析以及解决办法
本文出处:http://www.cnblogs.com/wy123/p/6238844.html 最近遇到一个存储过程在某些特殊的情况下,效率极其低效, 至于底下到什么程度我现在都没有一个确切的数据, ...
- c# Enumerable中Aggregate和Join的使用
参考页面: http://www.yuanjiaocheng.net/ASPNET-CORE/asp.net-core-environment.html http://www.yuanjiaochen ...
- 超详细mysql left join,right join,inner join用法分析
下面是例子分析表A记录如下: aID aNum 1 a20050111 2 a20050112 3 a20050113 4 ...
- join Linq
List<Publisher> Publishers = new List<Publisher>(); Publisher publish1 = new Publisher() ...
- mysql join 和left join 对于索引的问题
今天遇到一个left join优化的问题,搞了一下午,中间查了不少资料,对MySQL的查询计划还有查询优化有了更进一步的了解,做一个简单的记录: select c.* from hotel_info_ ...
- BCL中String.Join的实现
在开发中,有时候会遇到需要把一个List对象中的某个字段用一个分隔符拼成一个字符串的情况.比如在SQL语句的in条件中,我们通常需要把List<int>这样的对象转换为“1,2,3”这样的 ...
- [数据库基础]——图解JOIN
阅读导航 一.概要 二.JOIN分类 三.JOIN分类详解 一.概要 JOIN对于接触过数据库的人,这个词都不陌生,而且很多人很清楚各种JOIN,还有很多人对这个理解也不是很透彻,这次就说说JOIN操 ...
- Spark join 源码跟读记录
PairRDDFunctions类提供了以下两个join接口,只提供一个参数,不指定分区函数时默认使用HashPartitioner;提供numPartitions参数时,其内部的分区函数是HashP ...
随机推荐
- php开发入门教程
LAMP window:WAMP(windows,apache,mysql,php) LAMP是 Linux,Apache,MySQL和PHP的缩写,是我们提供 Web 服务的软件基础. 对于 Lin ...
- 【VB】操作ODBC-DAO方式操作只能查询,不能更新插入操作解决。
最近接手一个改善项目,需要从Access转化到SQL Server 2014,使用原有的ODBC连接方式只能查询,不能更新插入.网上一直找不到解决方案,然后自己测试一下使用ADO方式竟然可以连接了.具 ...
- temp 临时文件
放假了,放假了:http://blog.csdn.net/skywalker_only/article/details/17076851 nucht2.2.1爆出如下异常: Exception in ...
- Unity3D 3D横版跑酷
Unity3d 3D横版跑酷系列(Character Controller组件) @广州小龙 目前在做一个3D跑酷的横版游戏,目前说一下 Character Controller组件! 1.Slop ...
- unity3d中的http通信
转载 http://blog.csdn.net/mfc11/article/details/8188785的博客,如果侵权,请留言我及时删除! 前言 Unity3d 是一个跨平台的引擎,在移动互联网浪 ...
- Linux Kernel 本地拒绝服务漏洞
漏洞名称: Linux Kernel 本地拒绝服务漏洞 CNNVD编号: CNNVD-201308-090 发布时间: 2013-08-08 更新时间: 2013-08-08 危害等级: 漏洞类 ...
- 搜索(DLX):HDU 3663 Power Stations
Power Stations Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)To ...
- 【模拟】ECNA 2015 I What's on the Grille? (Codeforces GYM 100825)
题目链接: http://codeforces.com/gym/100825 题目大意: 栅栏密码.给定N(N<=10),密钥为一个N*N的矩阵,'.'代表空格可以看到,'X'代表被遮挡,还有密 ...
- QTP关于AOM的Javascript启动方式
序 QTP的AOM模型想必大家都很熟悉了,平时常用的就是通过VBS脚本的方式编写启动程序(也是我现在用的方法).其实,还有很多其他的方式,如Java,C#,JS,这些语言都是通过调用QTObjectM ...
- 如何解决升级WIN服务的时候,不暴力停止服务 达到升级的目的
同一个WIN服务,分别部署在A.B两台服务器上,前面使用netscaler负载均衡 ,A和B被请求频繁,几乎时时刻刻都被请求 .PS:发布WIN服务的正常流程是,停止WIN服务->发布WIN ...