SQL 连接和排除

Question

假设在 T-SQL 中有这样的查询。

   SELECT *  
     FROM Stock S    
LEFT JOIN StockBarcode SB ON SB.StockID = S.StockID
                         AND SB.ShopID = @ShopID 
                         AND SB.Inactive = 0    
LEFT JOIN StockBarcode SB1 ON SB1.StockID = S.StockID
                          AND SB1.ShopID = 0 
                          AND SB1.Inactive = 0    
    WHERE S.StockID = @StockID

我的理解是我可以这样重写查询

   SELECT * 
     FROM Stock S    
LEFT JOIN StockBarcode SB ON S.StockID = SB.StockID 
                         AND SB.ShopID = @ShopID    
LEFT JOIN StockBarcode SB1 ON S.StockID = SB1.StockID 
                          AND SB1.ShopID = 0     
    WHERE S.StockID = @StockID 
      AND ISNULL(SB.Inactive, 0) = 0 
      AND ISNULL(SB1.Inactive, 0) = 0

...结果是一样的。 (如果我错了请纠正我)哪个是最佳查询，为什么？如果我使用另一个数据库引擎(例如 MySql)，情况会有所不同吗？

提前感谢任何答案:-)

编辑:为了澄清，这里是整个查询，如果有帮助的话。

SELECT 
    SSCLRU.SupplierCode,  
    S.[Description],
    S.TaxRate AS GSTRate,
    ISNULL(ISNULL(SB.PackPrice, SB1.PackPrice), S.RRP) AS Price,
    ISNULL(SB.PackSize, SB1.PackSize) AS Quantity,
    ISNULL(SB.SalePrice, SB1.SalePrice) AS SalePrice,
    ISNULL(SB.SaleDateFrom, SB1.SaleDateFrom) AS SalePriceStartDate,
    ISNULL(SB.SaleDateTo, SB1.SaleDateTo) AS SalePriceEndDate
FROM Stock S

LEFT JOIN StockSupplierCodePreferredLastReceivedUnique SSCLRU ON
S.StockID = SSCLRU.StockID

LEFT JOIN StockBarcode SB ON
S.StockID = SB.StockID AND
SB.ShopID = @ShopID AND
SB.Inactive = 0

LEFT JOIN StockBarcode SB1 ON
S.StockID = SB1.StockID AND
SB1.ShopID = 0 AND
SB1.Inactive = 0

WHERE S.StockID = @StockID 

Answer 1

第一个更清晰，因为您不必担心 WHERE 中的不匹配行

但是，我可能会使用这个结构来完全分离连接和过滤条件

FROM
   Stock S
   LEFT JOIN
   StockSupplierCodePreferredLastReceivedUnique SSCLRU ON S.StockID = SSCLRU.StockID

   LEFT JOIN
   (
    SELECT StockID, ...
    FROM StockBarcode
    WHERE ShopID = @ShopID AND Inactive = 0
   ) SB ON S.StockID = SB.StockID

   LEFT JOIN
   (
    SELECT StockID, ...
    FROM StockBarcode
    WHERE ShopID = 0 AND Inactive = 0
   ) SB1 ON S.StockID = SB1.StockID
WHERE
   S.StockID = @StockID 

派生表也可以插入 CTE(或 2)。