Mysql CASE语句多列

Question

我有兴趣制作一个案例陈述,从两个不同的列中提取值,其中一个涉及计算.我不知道如何使这个工作,但我会告诉你到目前为止我有什么.(我有一列显示项目类型,例如特殊订单项目,已停产的物品和通常库存的物品.第二列显示现有数量 - 销售订单数量以确定物料是否有库存.)这是我的查询

SELECT ItemID, ItemType, (QuantityOnHand - QuantityonSalesOrders) AS Instock
CASE
WHEN ItemType = 'SP / OR' THEN 'Special Order' 
WHEN Instock < '1' THEN 'Out of Stock' 
WHEN Instock > '0' THEN 'In Stock' 
AS "Stock" FROM peachtree;

Answer 1

对于此类请求,您将不得不重用计算或使用子查询.这是因为您提供Instock值的别名无法在选择列表中使用:

SELECT ItemID, 
    ItemType, 
    Instock,
    CASE
        WHEN ItemType = 'SP / OR' THEN 'Special Order' 
        WHEN Instock < '1' THEN 'Out of Stock' 
        WHEN Instock > '0' THEN 'In Stock' 
    END AS "Stock" 
FROM
(
    select ItemID, ItemType, (QuantityOnHand - QuantityonSalesOrders) AS Instock
    from peachtree
) p;

要么:

SELECT ItemID, 
    ItemType, 
    (QuantityOnHand - QuantityonSalesOrders) as Instock,
    CASE
        WHEN ItemType = 'SP / OR' THEN 'Special Order' 
        WHEN (QuantityOnHand - QuantityonSalesOrders) < '1' THEN 'Out of Stock' 
        WHEN (QuantityOnHand - QuantityonSalesOrders) > '0' THEN 'In Stock' 
    END AS "Stock" 
FROM peachtree