LINQ查询与GROUP和SUM [英] LINQ Query with GROUP and SUM

问题描述

请帮我把我的头周围使用LINQ与A组和SUM查询。

  //查询数据库
IEnumerable的＆LT;＆畅销商品GT; best_sellers从BS =（db.MYDATABASE）。取（25）
                                       其中，bs.COMPANY ==我的公司
                                       通过bs.PROD code到G团BS
                                       排序依据g.Sum（g.MQTY）
                                       选择畅销书（）
                                       {
                                           product_ code =，
                                           PRODUCT_DESCRIPTION =，
                                           total_quantity =
                                      };
 

我想：

• 从db.MYDATABASE取前25个项目


• 集团所有结果通过bs.PROD code


• 的总和，每个bs.PROD code定购


• 凡公司是我公司


• 然后通过管道将在数据我畅销商品（）对象

我很困惑，因为只要添加我组中的组合，我的 BS 变量变得无用。

解决方案

  

我很困惑，因为只要添加我组的组合，我BS变量变得无用。

是的，因为你不再有一个单一的项目 - 你现在处理项目的集团的序列。您可以在第一项获得每个小组，我想会是在描述得到的有效方法是什么？

  VAR的查询=从BS在db.MYDATABASE.Take（25）
             其中，bs.COMPANY ==我的公司
             通过bs.PROD code到G团BS
             排序依据g.Sum（X =＆GT; x.MQTY）
             选择新的畅销商品
             {
                 product_ code = g.Key，
                 PRODUCT_DESCRIPTION = g.First（）描述，
                 total_quantity = g.Sum（X =＆GT; x.MQTY）
             };
 

请注意，如果没有指定的排序，从db.MYDATABASE排名前25位的项目是没有意义的。 顶部在哪些方面？你可能想：

 从酒店在db.MYDATABASE.OrderByDescending（X =＆GT; x.Price）。取（25）
 

或类似的东西。请注意，如果没有那些拥有公司的我的公司，你会没有结果落得...

或者，如果你想在排名前25位畅销书，你想在最后的拿的部分：

  VAR的查询=从db.MYDATABASE BS
             其中，bs.COMPANY ==我的公司
             通过bs.PROD code到G团BS
             排序依据g.Sum（X =＆GT; x.MQTY）降
             选择新的畅销商品
             {
                 product_ code = g.Key，
                 PRODUCT_DESCRIPTION = g.First（）描述，
                 total_quantity = g.Sum（X =＆GT; x.MQTY）
             };
VAR TOP25 = query.Take（25）;
 

Please help me to get my head around querying using LINQ with a GROUP and SUM.

// Query the database
IEnumerable<BestSeller> best_sellers = from bs in (db.MYDATABASE).Take(25)
                                       where bs.COMPANY == "MY COMPANY"
                                       group bs by bs.PRODCODE into g
                                       orderby g.Sum(g.MQTY)
                                       select new BestSeller()
                                       {
                                           product_code = ,
                                           product_description = ,
                                           total_quantity =  
                                      };

I wish to:

• Take the top 25 items from db.MYDATABASE
• Group all the results by bs.PRODCODE
• Order it by the sum total for each bs.PRODCODE
• Where the company is "MY COMPANY"
• Then pipe the data in to my BestSeller() objects

I'm confused, because as soon as I add my group in to the mix, my bs variable becomes useless.

解决方案

I'm confused, because as soon as I add my group in to the mix, my bs variable becomes useless.

Yes, because you no longer have a single item - you're now processing a sequence of groups of items. You can get at first item for each group, which I assume would be a valid way of getting at the description?

var query =  from bs in db.MYDATABASE.Take(25)
             where bs.COMPANY == "MY COMPANY"
             group bs by bs.PRODCODE into g
             orderby g.Sum(x => x.MQTY)
             select new BestSeller
             {
                 product_code = g.Key,
                 product_description = g.First().DESCRIPTION,
                 total_quantity = g.Sum(x => x.MQTY) 
             };

Note that without specifying an ordering, "the top 25 items from db.MYDATABASE" makes no sense. "Top" in what way? You may well want:

from bs in db.MYDATABASE.OrderByDescending(x => x.Price).Take(25)

or something similar. Note that if none of those have a company of "MY COMPANY" you'll end up with no results...

Or if you want the top 25 bestsellers, you want the "take" part at the very end:

var query =  from bs in db.MYDATABASE
             where bs.COMPANY == "MY COMPANY"
             group bs by bs.PRODCODE into g
             orderby g.Sum(x => x.MQTY) descending
             select new BestSeller
             {
                 product_code = g.Key,
                 product_description = g.First().DESCRIPTION,
                 total_quantity = g.Sum(x => x.MQTY) 
             };
var top25 = query.Take(25);

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