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Logical Expressions (XQuery)

  • Artikkeli

Applies to: SQL Server

XQuery supports the logical and and or operators.

expression1 and expression2  
expression1 or expression2

The test expressions, expression1,``expression2, in SQL Server can result in an empty sequence, a sequence of one or more nodes, or a single Boolean value. Based on the result, their effective Boolean value is determined in the following manner:

  • If the test expression results in an empty sequence, the result of the expression is False.

  • If the test expression results in a single Boolean value, this value is the result of the expression.

  • If the test expression results in a sequence of one or more nodes, the result of the expression is True.

  • Otherwise, a static error is raised.

The logical and and or operator is then applied to the resulting Boolean values of the expressions with the standard logical semantics.

The following query retrieves from the product catalog the front-angle small pictures, the <Picture> element, for a specific product model. Note that for each product description document, the catalog can store one or more product pictures with different attributes, such as size and angle.

SELECT CatalogDescription.query('  
     declare namespace PD="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";  
     for $F in /PD:ProductDescription/PD:Picture[PD:Size="small"   
                                                 and PD:Angle="front"]  
     return   
         $F   
    ') as Result  
FROM  Production.ProductModel  
where ProductModelID=19

This is the result:

<PD:Picture   
  xmlns:PD="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription">  
  <PD:Angle>front</PD:Angle>  
  <PD:Size>small</PD:Size>  
  <PD:ProductPhotoID>31</PD:ProductPhotoID>  
</PD:Picture>

See Also

XQuery Expressions