如何在子組上使用GroupBy

也許我正在談論這一切都是錯誤的，我是Linq的新手，但如果有人能夠幫助我，我會非常感激。以下是我的代碼。我正在試着對標題和詳細信息表中的信息進行一些總結。因此，我可以看到每個商家位置的總銷售量和總訪問量（單個交易）。詳細信息表將會將表頭中的1個事務拆分爲多行，因此1個事務標識可以在詳細信息表中多次出現。如何在子組上使用GroupBy

  var query2 = db.sales_transaction_header 
          .Join(db.sales_transaction_detail, 
           sth => sth.transaction_id, 
           std => std.transaction_id, 
           (sth, std) => new { TransHeader = sth, TransDetail = std }) 
         .GroupBy(x => x.TransHeader.merchant_location_id) 
         .Select(g => new MerchantConsumerSalesDTO 
         { 
          TotalSales = g.Sum(x => x.TransDetail.transaction_amount), 
          MerchantId = g.FirstOrDefault().TransHeader.merchant_location_id, 
          TotalVisits = g.GroupBy(x => x.TransHeader.transaction_id).Select(g2 => g2.Count()), 
         }) 
         .ToList();

TotalVisits給我各種問題！我本來試圖

TotalVisits = g.Select(x => x.TransHeader.transaction_id).Distinct().Count()

但是，這給了我莫名其妙的錯誤：

Unknown column 'Project3.merchant_location_id' in 'where clause'

沒有.Distinct（），它（）返回正確的計數，但它是錯誤的號碼！由於我只需要計算不同的值，但使用Distinct（）會給我一個錯誤！所以我嘗試在子組上使用GroupBy。這甚至不允許我編譯。我得到各種錯誤，如「不能隱式地將Ienumerable轉換爲int」或「無法將匿名類型轉換爲int」 - 我的智慧結束了！我只是完全錯誤的軌道，或者這是一個小而簡單的修復？

在此先感謝！

編輯： 也許這將有助於澄清我的意圖。我的表結構如下：

sales_transaction_header 
    transaction_id 
    merchant_location_id 
    card 
    transaction_date 

sales_transaction_detail 
    transaction_detail_id 
    transaction_id 
    transaction_amount 
    seat_nbr

所以，基本上單個事務可以分爲基礎上，seat_nbr多個詳細信息行。因此，如果我理解正確，第一個groupby應該只分組商戶ID，仍然留下多行用於單個交易。我需要另一組來計算唯一的事務id。正確？

而且，我生成的查詢低於：

SELECT `Project2`.`merchant_location_id`, 
     `Project2`.`c1`, 
     `Project2`.`merchant_location_id1`, 
     (SELECT Count(1) AS `A1` 
     FROM (SELECT DISTINCT `Extent7`.`transaction_id` 
       FROM `sales_transaction_header` AS `Extent7` 
         INNER JOIN `sales_transaction_detail` AS `Extent8` 
           ON `Extent7`.`transaction_id` = 
            `Extent8`.`transaction_id` 
       WHERE `Project2`.`merchant_location_id` = 
         `Extent7`.`merchant_location_id`) AS 
       `Distinct2`) AS `C2` 
FROM (SELECT `Apply1`.`merchant_location_id`, 
       `Apply1`.`merchant_location_id` 
         AS `merchant_location_id1`, 
       (SELECT Sum(`Extent6`.`transaction_amount`) AS `A1` 
       FROM `sales_transaction_header` AS `Extent5` 
         INNER JOIN `sales_transaction_detail` AS `Extent6` 
           ON `Extent5`.`transaction_id` = 
            `Extent6`.`transaction_id` 
       WHERE `Apply1`.`merchant_location_id` = 
         `Extent5`.`merchant_location_id`) AS 
       `C1` 
     FROM (SELECT `Distinct1`.`merchant_location_id`, 
         (SELECT `Extent3`.`transaction_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `transaction_id`, 
         (SELECT `Extent3`.`merchant_location_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `MERCHANT_LOCATION_ID1`, 
         (SELECT `Extent3`.`transaction_date` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `transaction_date`, 
         (SELECT `Extent3`.`post_date` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `post_date`, 
         (SELECT `Extent3`.`card_token` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `card_token`, 
         (SELECT `Extent3`.`transaction_type` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `transaction_type`, 
         (SELECT `Extent3`.`processed` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `processed`, 
         (SELECT `Extent3`.`partner_transaction_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `partner_transaction_id`, 
         (SELECT `Extent4`.`transaction_detail_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `transaction_detail_id`, 
         (SELECT `Extent4`.`transaction_id` AS `TRANSACTION_ID1` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `TRANSACTION_ID1`, 
         (SELECT `Extent4`.`transaction_amount` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `transaction_amount`, 
         (SELECT `Extent4`.`charity_location_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `charity_location_id`, 
         (SELECT `Extent4`.`event_type_id` 
         FROM `sales_transaction_header` AS `Extent3` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent4` 
             ON `Extent3`.`transaction_id` = 
              `Extent4`.`transaction_id` 
         WHERE `Distinct1`.`merchant_location_id` = 
           `Extent3`.`merchant_location_id` 
         LIMIT 1) AS `event_type_id` 
       FROM (SELECT DISTINCT `Extent1`.`merchant_location_id` 
         FROM `sales_transaction_header` AS `Extent1` 
           INNER JOIN `sales_transaction_detail` AS 
              `Extent2` 
             ON `Extent1`.`transaction_id` = 
              `Extent2`.`transaction_id`) AS 
         `Distinct1`) AS `Apply1`) AS `Project2`

UPDATE：

var query = db.sales_transaction_header .Join(db.sales_transaction_detail, sth => sth.transaction_id, std => std.transaction_id, (sth, std) => new { TransHeader = sth, TransDetail = std }) .GroupBy(x => x.TransHeader.merchant_location_id) .ToList() .Select(g => new MerchantConsumerSalesDTO { TotalSales = g.Sum(x => x.TransDetail.transaction_amount), MerchantId = g.Key, TotalConsumerVisits = g.GroupBy(x => x.TransHeader.transaction_id).Count(), });

這是由於MySQL數據庫的限制：

最終，我去我正在使用 - 它在MSSQL中工作很好，顯然無需使用ToList（），但至少現在它正在工作！感謝這麼多，ROB！

來源

2016-03-17 user2480201

MERCHANTID應'g.Key'。儘管它們在語義上是相同的，但它更清晰。 TotalVisits應該只是'g.Count（）'（你已經分組了）或'g.Distinct（）。Count（）'。不過，在分組之前做清楚可能會更好。 – Rob

在代碼的'.Select'部分，編譯器說每個變量是什麼（即'TotalSales'，'MerchantID'，'TotalVisits'）......當你用光標懸停在它們上時？（假設你正在使用VS） –

我相信你錯過了where子句。看看這[其他stackoverflow答案]（http://stackoverflow.com/questions/2767709/c-sharp-joins-where-with-linq-and-lambda）瞭解更多信息。 –

經過在chat的討論後，結果發現該行爲是由於MySql連接器中的一個錯誤。

以下代碼獲取解決此bug通過內存評估組：

var query = db.sales_transaction_header 
    .Join(db.sales_transaction_detail, 
     sth => sth.transaction_id, 
     std => std.transaction_id, 
     (sth, std) => new {TransHeader = sth, TransDetail = std}) 
    .GroupBy(x => x.TransHeader.merchant_location_id) 
    .ToList() 
    .Select(g => new MerchantConsumerSalesDTO 
    { 
     TotalSales = g.Sum(x => x.TransDetail.transaction_amount), 
     MerchantId = g.Key, 
     TotalConsumerVisits = g.GroupBy(x => x.TransHeader.transaction_id).Count(), 
    });

這是因爲它會產生以下代碼：

SELECT `GroupBy1`.`k1`  AS `merchant_location_id`, 
     `GroupBy1`.`a1`  AS `C1`, 
     (SELECT Count(1) AS `A1` 
     FROM (SELECT DISTINCT `Extent3`.`transaction_id` 
       FROM `sales_transaction_header` AS `Extent3` 
         INNER JOIN `sales_transaction_detail` AS `Extent4` 
           ON `Extent3`.`transaction_id` = 
            `Extent4`.`transaction_id` 
       WHERE `GroupBy1`.`k1` = `Extent3`.`merchant_location_id`) AS 
       `Distinct1`) AS `C2` 
FROM (SELECT `Extent1`.`merchant_location_id` AS `K1`, 
       Sum(`Extent2`.`transaction_amount`) AS `A1` 
     FROM `sales_transaction_header` AS `Extent1` 
       INNER JOIN `sales_transaction_detail` AS `Extent2` 
         ON `Extent1`.`transaction_id` = 
          `Extent2`.`transaction_id` 
     GROUP BY `Extent1`.`merchant_location_id`) AS `GroupBy1`

在MySQL，內選擇不能引用外部結果，所以這行：

`GroupBy1`.`k1` = `Extent3`.`merchant_location_id`

失敗，因爲GroupBy1是在選擇的範圍之外。

解決方法是在組後添加ToList()，使得最終的選擇（和求和）完成內存

來源

2016-03-18 00:15:40 Rob

謝謝 - 實際上我已經嘗試了最後一個groupby（）。count（），它是給我「where column中的unknown column merchant_location_id」的錯誤。TotalVisits是總數然而，由於交易ID可以出現多次，即使在第一組之後（key = merchant id），我仍然需要以某種方式清除倍數。是否有另一種方法可以超出最後的建議？ – user2480201

@ user2480201這很奇怪 - 它應該能夠處理它。你能發佈生成的SQL代碼嗎？ – Rob

Let me al所以張貼表格，可能會更清楚。我在哪裏可以獲得生成的代碼？我知道我可以在VS中進行調試時查看它，但它不允許我選擇/複製它。 – user2480201

如何在子組上使用GroupBy

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