指令 该指令是用来处理那些不想返回结果的列,许多人会有疑问觉得没有必要,只要在列中不增加就行了,条件和排序也可以直接使用列。我们可以想得到使用UNION ALL时就用得上了,看下面的例子。 查询语句: SELECT 1 AS Tag,NULL AS Parent, CategoryID AS [Category!1!ID!hide], CategoryName AS [Category!1!Name], NULL AS [Product!2!ProductID!element], NULL AS [Product!2!ProductName!element] FROM Categories WHERE CategoryID < 3 UNION ALL SELECT 2 ,1 , Categories.CategoryID, NULL, ProductID, ProductName FROM Categories JOIN Products ON Categories.CategoryID = Products.CategoryID AND ProductID <5 WHERE Categories.CategoryID < 3 ORDER BY [Category!1!ID!hide] DESC,[Product!2!ProductID!element] ASC FOR XML EXPLICIT 返回结果: <Category Name="Condiments"> <Product> <ProductID>3</ProductID> <ProductName>Aniseed Syrup</ProductName> </Product> <Product>
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