使用JOIN和GROUP的SQLite SELECT？

Question

我正在尝试根据以下字符串的结果添加一列：

SELECT product_code AS "Product Code", SUM(quantity) AS "Quantity" 
FROM receipts_items
GROUP BY product_code
ORDER BY SUM(quantity) DESC

这个字符串给了我一个产品代码和销售数量。 根据产品代码，我需要添加的是产品代码的描述。

product_code和description列在同一个表中“products”数量在另一个表“receipts_items”中

谢谢！！！

Answer 1

您想在product_code上JOIN两个表。

您确实应该执行LEFT JOIN以捕获没有关联收据项的产品，然后在SUM放入CASE语句以将NULL值减少为0。

SELECT p.product_code AS "Product Code",
    p.description AS "Description", 
    SUM(CASE WHEN ri.quantity IS NULL THEN 0 ELSE ri.quantity END) AS "Quantity" 
FROM products AS p
    LEFT JOIN receipts_items AS ri ON ri.product_code = p.product_code
GROUP BY p.product_code
ORDER BY SUM(ri.quantity) DESC