The Best Way to shred XML data into SQL Server database columns

Question

What is the best way to shred XML data into various database columns? So far I have mainly been using the nodes and value functions like so:

INSERT INTO some_table (column1, column2, column3)
SELECT
Rows.n.value('(@column1)[1]', 'varchar(20)'),
Rows.n.value('(@column2)[1]', 'nvarchar(100)'),
Rows.n.value('(@column3)[1]', 'int'),
FROM @xml.nodes('//Rows') Rows(n)

However I find that this is getting very slow for even moderate size xml data.

Answer 1

Stumbled across this question whilst having a very similar problem, I'd been running a query processing a 7.5MB XML file (~approx 10,000 nodes) for around 3.5~4 hours before finally giving up.

However, after a little more research I found that having typed the XML using a schema and created an XML Index (I'd bulk inserted into a table) the same query completed in ~ 0.04ms.

How's that for a performance improvement!

Code to create a schema:

IF EXISTS ( SELECT * FROM sys.xml_schema_collections where [name] = 'MyXmlSchema')
DROP XML SCHEMA COLLECTION [MyXmlSchema]
GO

DECLARE @MySchema XML
SET @MySchema = 
(
    SELECT * FROM OPENROWSET
    (
        BULK 'C:PathToSchemaMySchema.xsd', SINGLE_CLOB 
    ) AS xmlData
)

CREATE XML SCHEMA COLLECTION [MyXmlSchema] AS @MySchema 
GO

Code to create the table with a typed XML column:

CREATE TABLE [dbo].[XmlFiles] (
    [Id] [uniqueidentifier] NOT NULL,

    -- Data from CV element 
    [Data] xml(CONTENT dbo.[MyXmlSchema]) NOT NULL,

CONSTRAINT [PK_XmlFiles] PRIMARY KEY NONCLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

Code to create Index

CREATE PRIMARY XML INDEX PXML_Data
ON [dbo].[XmlFiles] (Data)

There are a few things to bear in mind though. SQL Server's implementation of Schema doesn't support xsd:include. This means that if you have a schema which references other schema, you'll have to copy all of these into a single schema and add that.

Also I would get an error:

XQuery [dbo.XmlFiles.Data.value()]: Cannot implicitly atomize or apply 'fn:data()' to complex content elements, found type 'xs:anyType' within inferred type 'element({http://www.mynamespace.fake/schemas}:SequenceNumber,xs:anyType) ?'.

if I tried to navigate above the node I had selected with the nodes function. E.g.

SELECT
    ,C.value('CVElementId[1]', 'INT') AS [CVElementId]
    ,C.value('../SequenceNumber[1]', 'INT') AS [Level]
FROM 
    [dbo].[XmlFiles]
CROSS APPLY
    [Data].nodes('/CVSet/Level/CVElement') AS T(C)

Found that the best way to handle this was to use the OUTER APPLY to in effect perform an "outer join" on the XML.

SELECT
    ,C.value('CVElementId[1]', 'INT') AS [CVElementId]
    ,B.value('SequenceNumber[1]', 'INT') AS [Level]
FROM 
    [dbo].[XmlFiles]
CROSS APPLY
    [Data].nodes('/CVSet/Level') AS T(B)
OUTER APPLY
    B.nodes ('CVElement') AS S(C)

Hope that that helps someone as that's pretty much been my day.