mysql - 替换从左外连接返回的默认空值

Question

我有一个 Microsoft SQL Server 2008 查询，它使用左外连接从三个表中返回数据。很多时候，第二个和第三个表中没有数据，所以我得到一个空值，我认为这是左外连接的默认值。有没有办法替换 select 语句中的默认值？我有一个解决方法，我可以选择一个表变量，但感觉有点脏。

SELECT iar.Description, iai.Quantity, iai.Quantity * rpl.RegularPrice as 'Retail', 
iar.Compliance FROM InventoryAdjustmentReason iar
LEFT OUTER JOIN InventoryAdjustmentItem iai  on (iar.Id = iai.InventoryAdjustmentReasonId)
LEFT OUTER JOIN Item i on (i.Id = iai.ItemId)
LEFT OUTER JOIN ReportPriceLookup rpl on (rpl.SkuNumber = i.SkuNo)
WHERE iar.StoreUse = 'yes'

如果可能，我希望 Quantity 和 RegularPrice 默认为零。

Answer 1

就这么简单

IsNull(FieldName, 0)

或更完整地说:

SELECT iar.Description, 
  ISNULL(iai.Quantity,0) as Quantity, 
  ISNULL(iai.Quantity * rpl.RegularPrice,0) as 'Retail', 
  iar.Compliance 
FROM InventoryAdjustmentReason iar
LEFT OUTER JOIN InventoryAdjustmentItem iai  on (iar.Id = iai.InventoryAdjustmentReasonId)
LEFT OUTER JOIN Item i on (i.Id = iai.ItemId)
LEFT OUTER JOIN ReportPriceLookup rpl on (rpl.SkuNumber = i.SkuNo)
WHERE iar.StoreUse = 'yes'