mysql 查詢 - 使用內部聯接顯示 mysql 結果時出錯

Question

我有 2 個要合並的表。 我想打印所有產品及其相應的總數量和總金額。

這就是我所擁有的。

//Product Table 
productID    productName
   1              A
   2              B
   3              C


//Order Record (This came from 2 tables that I have successfully merged)
orderID     productID     quantity     amount
   1            1             5         100
   2            2             2         50
   3            2             3         150             

我想做這個

productID     productName     totalQuantity     totalAmount
    1             A                 8               250
    2             B                 2                50
    3             C                 0                0      
//instead of 0 for total Quantity and total Amount, it shows 2 and 50 respectively.

這是我的 php 代碼。 它正確輸出了前 2 行（產品 A 和 B）的數據，但是當涉及到最后一行（產品 C）時，它復制了產品 B 的數據。請告訴我我的代碼有什么問題？ 先感謝您。

$products = $wpdb->get_results("SELECT * FROM wp_products");

foreach($products as $product){
   $productID = $product->productID; 
   $productName = $product->productName;

   $orders = $wpdb->get_results("SELECT a.productID, SUM(a.quantity) as totalQuantity, SUM(a.amount) as totalSales FROM a INNER JOIN b ON a.orderID = b.orderID GROUP BY productID");

   if(is_null($orders)){
      $totalQuantity = 0;
      $totalSales = '0.00';
   }

   foreach($orders as $order){
      $totalQuantity = $order->totalQuantity; 
      $totalSales = $order->totalSales; 
   }

   $orderItem = array(
                        'productID' => $productID,
                        'productName' => $productName,
                        'totalQuantity' => $totalQuantity,
                        'totalSales' => $totalSales
                     );
               $records[] = $orderItem;
}

Answer 1

快速修復是（只需將WHERE添加到您的查詢中）：

$orders = $wpdb->get_results("SELECT 
        a.productID, 
        SUM(a.quantity) as totalQuantity, 
        SUM(a.amount) as totalSales 
        FROM a 
        INNER JOIN b 
        ON a.orderID = b.orderID 
        WHERE a.productID = $productID
        GROUP BY productID");

但是看看你的片段，我相信你可以將它簡化（替換完整片段）：

$records = $wpdb->get_results("SELECT 
       p.productID, 
       p.productName, 
       COALESCE(SUM(a.quantity),0) as totalQuantity, 
       COALESCE(SUM(a.amount),0) as totalSales
     FROM wp_products p
     LEFT JOIN a 
     GROUP BY p.productID");

Answer 2

我不相信您的查詢是正確的。

我沒有看到表名。 嘗試將其更改為：

FROM `tablename` AS a INNER JOIN `othertable` AS b

用表 a 和 b 的名稱交換表名和其他表。