是否可以使用一个 SQL 来使用自定义列的自定义数据 [关闭]

Question

是否有可能从 2 个表中得到这样的结果： ps：1号仓库，……我的意思是我所有的仓库

现在我正在执行一个 for 循环并为每个 sku 获取数据，如下所示：

首先从 products 表中获取所有产品：

SELECT id, sku FROM products

然后对此做一个for循环：

SELECT ware.id, ware.name, ware_inv.available as inventory,
ware_inv.id as inventoryName, ware.country
FROM warehouses as ware JOIN warehouse_inventory as ware_inv
ON ware.id = ware_inv.warehouse_id
WHERE ware.store_id = $1
AND ware_inv.sku = $2

仓库表架构：

仓库库存表架构：

warehouse_inventory 中的warehouse_id 是仓库表的外键。

Answer 1

条件聚合是一种适用于大多数 RDBMS 的旋转方式。

SELECT product.sku, warehouse.store_id
, SUM(CASE WHEN warehouse.name = 'warehouse 1' THEN inventory.available END) AS "warehouse 1"
, SUM(CASE WHEN warehouse.name = 'warehouse 2' THEN inventory.available END) AS "warehouse 2"
, SUM(CASE WHEN warehouse.name = 'warehouse 3' THEN inventory.available END) AS "warehouse 3"
, SUM(CASE WHEN warehouse.name = 'warehouse 4' THEN inventory.available END) AS "warehouse 4"
, SUM(inventory.available) AS "available"
FROM products AS product
LEFT JOIN warehouse_inventory AS inventory 
  ON inventory.sku = product.sku
LEFT JOIN warehouses AS warehouse
  ON warehouse.id = inventory.warehouse_id
WHERE product.sku = $2
  AND (warehouse.store_id = $1 OR warehouse.id IS NULL)
GROUP BY product.sku, warehouse.store_id

因为它在产品上留下了连接，这甚至会显示在任何仓库中都不可用的 sku。