XML DML UPDATING XML COLUMNS implementation of XQuery) inside

XML DML UPDATING XML COLUMNS implementation of XQuery) inside SQL Server. With the client-side implementation of XQuery, the input, document, and collection functions are supported, and multiple documents (or multiple instances of the XML data type) can be passed in as input parameters to a .NET stored procedure. We ll look at the .NET client XML APIs in Chapter 13. XML DML Updating XML Columns One thing that was left out of the XQuery 1.0 specification was a definition of an XQuery syntax for mutating XML instances or documents in place. A data manipulation language (DML) is not planned for the first version of XQuery, but a working draft is under development. Because SQL Server 2005 will use XQuery as the native mechanism for querying the XML data type inside the server, it is required to have some sort of manipulation language. The alternative would be to only be able to replace the instance of the XML type as an entire entity. Since changes to XML data type instances should participate in the current transaction context, this would be equivalent to using SELECT and INSERT in SQL without having a corresponding UPDATEstatement. Therefore, SQL Server 2005 introduces a heretofore nonstandard implementation of XML DML. XML DML is implemented using XQuery-like syntax with SQL-like extensions. This emphasizes the fact that manipulating an XML instance inside SQL Server is equivalent to manipulating a complex type or, more accurately, a graph of complex types. You invoke XML DML by using the xml.modifyfunction on a single XMLdata type column, variable, or procedure parameter. You use XML DML within the context of a SQL SET statement, using either UPDATE…SETon an XMLdata type column or using SET on an XML variable or parameter. As a general rule, it would look like this. change the value of XML data type column instance UPDATE some_table SET xml_col.modify( some XML DML ) WHERE id = 1 change the value of an XML variable DECLARE @x XML initialize it SET @x = initial XML now, mutate it SET @x = @x.modify( some XML DML ) Note that this syntax is used only to modify the XML nodes contained in an existing instance of an XML data type. To change a value to or from

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