SQL查询不产生任何结果

Question

我试图让这个查询工作：

SELECT Stock.*, 
     StockFeatures.Features, 
     StockDescriptions.Detailed, 
     StockDescriptions.Technical, 
     PRD1.RuleValue as Price, 
     PRD2.RuleValue as WasPrice, 
     PRD2.RuleValue-PRD1.RuleValue as Save, 
     PRD1.Quantity 
FROM 
    StockFeatures, Stock INNER JOIN 
    PriceRuleDetail PRD1 ON PRD1.Sku = Stock.Sku 
     AND PRD1.PriceRule = 'RG' LEFT JOIN 
    PriceRuleDetail PRD2 ON PRD2.Sku = Stock.Sku 
     AND PRD2.PriceRule = 'RRP' LEFT JOIN 
    StockDescriptions ON StockDescriptions.Sku = Stock.Sku 
WHERE Stock.GeneralStkStatus < 3 
AND Stock.Sku = '11044' 
AND StockFeatures.Sku = Stock.Sku 
ORDER BY PRD1.Quantity ASC 

它时，没有一个StockFeatures.Features行的StockFeatures表不返回任何结果 - 这也经常不会是。我该如何使它只在该表中没有任何内容时才会出现NULL值？

该表具有Sku和特征（Sku应与Stock.Sku列链接）列。

任何帮助，将不胜感激。

在此先感谢。

Answer 1

您需要LEFT JOIN至StockFeatures。

例如：（未经测试）

SELECT Stock.*, 
     StockFeatures.Features, 
     StockDescriptions.Detailed, 
     StockDescriptions.Technical, 
     PRD1.RuleValue as Price, 
     PRD2.RuleValue as WasPrice, 
     PRD2.RuleValue-PRD1.RuleValue as Save, 
     PRD1.Quantity 
FROM 
    Stock LEFT JOIN 
    StockFeatures ON Stock.Sku = StockFeatures.Sku INNER JOIN 
    PriceRuleDetail PRD1 ON PRD1.Sku = Stock.Sku 
     AND PRD1.PriceRule = 'RG' LEFT JOIN 
    PriceRuleDetail PRD2 ON PRD2.Sku = Stock.Sku 
     AND PRD2.PriceRule = 'RRP' LEFT JOIN 
    StockDescriptions ON StockDescriptions.Sku = Stock.Sku 
WHERE Stock.GeneralStkStatus < 3 
AND Stock.Sku = '11044' 
ORDER BY PRD1.Quantity ASC