The OPENXML function in SQL Server is used to parse XML data and retrieve information from it. This function provides an efficient way to query XML data, allowing you to treat the XML structure similarly to a relational format.
Here's a basic guide on how to use OPENXML to parse XML data:
Steps to Use OPENXML
1. Declare the XML Variable: First, you need to have your XML data in a variable.
2. Use the sp_xml_preparedocument Stored Procedure: This procedure prepares the XML document for use with the OPENXML function and returns a handle.
3. Use OPENXML with the Handle: Call the OPENXML function using the document handle you got in the previous step.
4. Select Data: Extract required fields from the XML structure.
5. Clean Up: Finally, free the XML document when you are done using the sp_xml_removedocument stored procedure.
Example
Here is an example that illustrates how to use OPENXML to parse XML data:
Sample XML Data
Let's say we have the following XML data:
<Books>
<Book>
<Title>Effective SQL</Title>
<Author>John Doe</Author>
<Year>2020</Year>
</Book>
<Book>
<Title>Learning XML</Title>
<Author>Jane Smith</Author>
<Year>2021</Year>
</Book>
</Books>
SQL Script
Here's how you can parse this XML:
DECLARE @xmlData XML;
SET @xmlData = '
<Books>
<Book>
<Title>Effective SQL</Title>
<Author>John Doe</Author>
<Year>2020</Year>
</Book>
<Book>
<Title>Learning XML</Title>
<Author>Jane Smith</Author>
<Year>2021</Year>
</Book>
</Books>';
-- Step 1: Prepare the XML document
DECLARE @docHandle INT;
EXEC sp_xml_preparedocument @docHandle OUTPUT, @xmlData;
-- Step 2: Use OPENXML to parse the XML
SELECT
Title,
Author,
Year
FROM OPENXML(@docHandle, '/Books/Book', 2)
WITH (
Title NVARCHAR(100) 'Title',
Author NVARCHAR(100) 'Author',
Year INT 'Year'
);
-- Step 3: Remove the XML document
EXEC sp_xml_removedocument @docHandle;
Explanation:
- Preparation: The XML data is stored in the @xmlData variable and prepared with sp_xml_preparedocument to generate a handle.
- Parsing: The OPENXML function is called with the handle and a specified XPath to navigate through the XML structure, retrieving the Title, Author, and Year of each Book.
- Cleanup: Finally, sp_xml_removedocument cleans up the resources used by the document handle.
Important Notes:
- The WITH clause is used to define the structure of your output variables and should match the XML structure you are working with.
- The 2 parameter in the OPENXML call specifies that the function should return attributes as columns, while child nodes would be treated as rows.
- SQL Server has more recent XML functionalities (like XQuery or nodes()) that can be easier to use and are more efficient. It's often recommended to use those for new development if you have a more recent version of SQL Server.
This is the fundamental process for using OPENXML to parse XML data in SQL Server. Make sure to refer to the SQL Server documentation for more details on handling XML and any additional features that are available in your version.