返回特定列的情况

Question

目标

如果产品是商品并且价格最低，则返回特定列。

问题

我正在创建一个产品价格比较应用程序。我已经获得了产品清单和特定产品的最低价格。但是，在一天之内，产品可以设置为报价，并且具有所有其他产品的最低价格。当发生这种情况时，我必须向用户确认这样的信息 - 带有标志或类似的东西。

我正在考虑使用查询本身来做这个行为 - 但我不知道，有时似乎这种做法不一致，因为如果产品没有发售，不知道我将如何在C＃中处理这个问题那将等待productState列。我需要建议（当然还有语法，因为我不知道[再次]）。

详细

我正在使用C＃.NET + MVC 4 + MySQL +实体框架5 +存储过程+ Razor引擎。

以下片段返回产品清单的最低价格以进行比较：

Min(Case When marketProducts.ProductPromotionalPrice = 0
    Then 
       marketProducts.ProductOriginalPrice 
    Else
       Least(
        marketProducts.ProductPromotionalPrice,
        marketProducts.ProductOriginalPrice
       )End) As minProductPrice,

但是，我想做这样的事情（当然 - 语法错误，但“有效”来说明）：

Min(Case When marketProducts.ProductPromotionalPrice = 0
    Then 
       marketProducts.ProductOriginalPrice 
    Else
       marketProducts.ProductState = 1 As productState, /* 
                                                           This is a normal
                                                           column.
                                                           1 means that 
                                                           the product is on 
                                                           offer.
                                                        */
       Least(
        marketProducts.ProductPromotionalPrice,
        marketProducts.ProductOriginalPrice
       )End) As minProductPrice,

完整查询：

CREATE DEFINER=`root`@`localhost` PROCEDURE `getProductsList`(IN `categoryId` INT, IN `productState` INT)
    LANGUAGE SQL
    NOT DETERMINISTIC
    CONTAINS SQL
    SQL SECURITY DEFINER
    COMMENT ''
BEGIN
    Select product.Id As productId,
        product.Name As productName,
        Min(Case When marketProducts.ProductPromotionalPrice = 0
            Then marketProducts.ProductOriginalPrice Else
            Least(marketProducts.ProductPromotionalPrice, marketProducts.ProductOriginalPrice)
            End) As minProductPrice,
            measure.Name As measureName,
            measure.Abbreviation As measureAbbreviation,
            productsImages.ProductImageThumbnail As thumbnailUrl,
            product.InMarketsQuantity as numberOfMarketsThatHaveThisProduct
    From bm_market_products as marketProducts
    Join bm_products As product On marketProducts.ProductId = product.Id
    Join bm_categories As category On product.CategoryId = category.Id
    Join bm_measures As measure On product.MeasureId = measure.Id
    Join bm_products_images As productsImages On product.Id = productsImages.ProductId
    WHERE (productState Is Null Or marketProducts.ProductState = productState)
    And (categoryId Is Null Or category.Id = categoryId)
    Group By marketProducts.ProductId;
END

此程序返回以下内容：

有什么想法吗？

Answer 1

你的语法错误的原因是你有时会在一个空格中填充两列。解决方案是始终具有如下所示的两列：

Select product.Id As productId,
    product.Name As productName,
    Min(Case When marketProducts.ProductPromotionalPrice = 0
        Then marketProducts.ProductOriginalPrice Else
        Least(marketProducts.ProductPromotionalPrice, marketProducts.ProductOriginalPrice)
        End) As minProductPrice,
    Min(Case When marketProducts.ProductPromotionalPrice = 0
            and marketProducts.ProductPromotionalPrice < marketProducts.ProductOriginalPrice
        Then 0 Else 1
        End) As productState,
        measure.Name As measureName,
        measure.Abbreviation As measureAbbreviation,
        productsImages.ProductImageThumbnail As thumbnailUrl,
        product.InMarketsQuantity as numberOfMarketsThatHaveThisProduct
From bm_market_products as marketProducts
Join bm_products As product On marketProducts.ProductId = product.Id
Join bm_categories As category On product.CategoryId = category.Id
Join bm_measures As measure On product.MeasureId = measure.Id
Join bm_products_images As productsImages On product.Id = productsImages.ProductId
WHERE (productState Is Null Or marketProducts.ProductState = productState)
And (categoryId Is Null Or category.Id = categoryId)
Group By marketProducts.ProductId;