Example: Specifying the HIDE Directive

This example illustrates the use of the HIDE directive. This directive is useful when you want the query to return an attribute for ordering the rows in the universal table that is returned by the query, but you do not want that attribute in the final resulting XML document.

This query constructs this XML:

<ProductModel ProdModelID="19" Name="Mountain-100">
  <Summary>
    <SummaryDescription>
           <Summary> element from XML stored in CatalogDescription column
    </SummaryDescription>
  </Summary>
</ProductModel>

This query generates the XML you want. The query identifies two column groups having 1 and 2 as Tag values in the column names.

This query uses the query() Method (xml Data Type) of the xml data type to query the CatalogDescription column of xml type in order to retrieve the summary description. The query also uses the value() Method (xml Data Type) of the xml data type to retrieve the ProductModelID value from the CatalogDescription column. This value is not required in the resulting XML, but is required to sort the resulting rowset. Therefore, the column name, [Summary!2!ProductModelID!HIDE], includes the HIDE directive. If this column is not included in the SELECT statement, you will have to sort the rowset by [ProductModel!1!ProdModelID] and [Summary!2!SummaryDescription] that is xml type and you cannot use the xml type column in ORDER BY. Therefore, the additional [Summary!2!ProductModelID!HIDE] column is added and is then specified in the ORDER BY clause.

SELECT  1 as Tag,
        0 as Parent,
        ProductModelID     as [ProductModel!1!ProdModelID],
        Name               as [ProductModel!1!Name],
        NULL               as [Summary!2!ProductModelID!hide],
        NULL               as [Summary!2!SummaryDescription]
FROM    Production.ProductModel
WHERE   CatalogDescription is not null
UNION ALL
SELECT  2 as Tag,
        1 as Parent,
        ProductModelID,
        Name,
        CatalogDescription.value('
         declare namespace PD="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
       (/PD:ProductDescription/@ProductModelID)[1]', 'int'),
        CatalogDescription.query('
         declare namespace pd="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
         /pd:ProductDescription/pd:Summary')
FROM    Production.ProductModel
WHERE   CatalogDescription is not null
ORDER BY [ProductModel!1!ProdModelID],[Summary!2!ProductModelID!hide]
FOR XML EXPLICIT
go

This is the result:

<ProductModel ProdModelID="19" Name="Mountain-100">
  <Summary>
    <SummaryDescription>
      <pd:Summary xmlns:pd="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription" >
        <p1:p xmlns:p1="http://www.w3.org/1999/xhtml">Our top-of-the-line competition mountain bike. Performance-enhancing options include the innovative HL Frame, super-smooth front suspension, and traction for all terrain. </p1:p>
      </pd:Summary>
    </SummaryDescription>
  </Summary>
</ProductModel>