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XML Jumpstart Workbench
27 June 2007
/* Some of the frustration of learning XML is in not being able to see clearly an entire process. So many of the existing manuals concentrate on just one step in a chain and leave the reader saying 'very technological. So what?'
In other cases, XML is used in illustrations with tiny fragments of real data, losing sight of the great value of XML as a means of exchanging large amounts of information
We'll try to take a different approach here in order to give it all some purpose. We're not going to even try to provide anything comprehensive here, more of a quick spin around the block
OK. Let's assume that we want an application which seeks to list out the nearest hundred pubs to any postcode in Britain. (apologies to our many friends outside Britain).
We have two XML files that gives the raw data, collected from several Publicly available sources. they are supplied with the article. One gives the location of every 'outcode', and the other every pub, with their postcode. Tantalising?
In this Workbench we will
Read an XML file into a SQL Server XML Variable
Shred a document fragment in an XML variable into a SQL Server table
Query a the contents of an XML variable for a set of values as an XML result
Assign the result of a SQL query to an XML variable
Store the contents of an XML variable to a table
Save an XML document fragment to a file.
Let's read the XML location information from a file into a table!
Reading an XML file into a SQL Server XML Variable
--------------------------------------------------
Assume we have the XML file unzipped in C:\workbench\locations.xml. The
files can be downloaded from the links at the top of the page in the Speech
bubble. ('UK Locations XML Xipped' and 'UK Pubs XML Zipped')
The data is over a Mb in size, so be warned! You'll need to unzip
them too!
First pull the file into a conventional relational table...
*/
DECLARE @xmlLocations XML
SELECT @xmlLocations = BulkColumn
FROM OPENROWSET(BULK 'C:\workbench\locations.xml', SINGLE_BLOB) AS x
/* we can store this XML data in a table with an XML column */
CREATE TABLE xTable
(
xTable_ID INT IDENTITY
PRIMARY KEY,
xCol XML
) ;
/* we then insert a row into the table from the XML variable */
INSERT INTO xTable ( xCol )
SELECT @xmlLocations
/*
Shredding a document fragment in an XML variable into a SQL Server table
------------------------------------------------------------------------
now we'll put it into a conventional table for working on. First
we define it */
CREATE TABLE [dbo].[location]
(
[location_ID] [int] IDENTITY(1, 1)
NOT NULL,
[whereabouts] [varchar](100) NULL,
[Town] [varchar](80) NULL,
[city] [varchar](80) NULL,
[county] [varchar](40) NULL,
[region] [varchar](40) NULL,
[outcode] [varchar](4) NULL,
[x] [int] NULL,
[y] [int] NULL,
[latitude] [numeric](18, 3) NULL,
[longitude] [numeric](18, 3) NULL
)
ON [PRIMARY]
/* and now we can simply shred the XML data type that we've read in
into the table, using the XML Data type nodes() method. */
INSERT INTO location
(
whereabouts,
town,
city,
county,
region,
outcode,
x,
y,
latitude,
Longitude
)
SELECT x.location.value(
'whereabouts[1]', 'varchar(100)') AS whereabouts,
x.location.value(
'town[1]', 'varchar(80)') AS town,
x.location.value(
'city[1]', 'varchar(80)') AS city,
x.location.value(
'county[1]', 'varchar(40)') AS county,
x.location.value(
'region[1]', 'varchar(40)') AS region,
x.location.value(
'outcode[1]', 'varchar(4)') AS outcode,
x.location.value(
'x[1]', 'int') AS x,
x.location.value(
'y[1]', 'int') AS y,
x.location.value(
'latitude[1]', 'numeric(18, 3) ') AS latitude,
x.location.value(
'longitude[1]', 'numeric(18, 3)') AS longitude
FROM @xmlLocations.nodes('//locations/location')
AS x ( location )
/* now we can try it out by finding the nearest places to a particular
postcode*/
GO
CREATE PROCEDURE spWhereIsThis @Postcode VARCHAR(10)
/*
spWhereIsThis 'cm2'
*/
AS
DECLARE @x INT,
@y INT
SELECT TOP 1--find out our coordinates
@x = x,
@y = y
FROM location
WHERE outcode LIKE RTRIM(LEFT(SUBSTRING(@Postcode, 1,
CHARINDEX(' ', @Postcode + ' ',
1) - 1), 4))
IF @@Rowcount = 0 --typo!
BEGIN
RAISERROR ( 'I don''t recognise the postcode ''%s''', 16, 1,
@postcode )
RETURN 1
END
SELECT TOP 100--list the 100 nearest locations
whereabouts,
region,
[miles] = ROUND(SQRT(SQUARE(X - @X) + SQUARE(Y - @Y))
* 0.0006214,0)
FROM location
WHERE x IS NOT NULL
ORDER BY miles
GO
/*
Querying the contents of an XML variable for a set of values as an XML result
----------------------------------------------------------------------------
we can extract data directly from the XML column if we wish
*/
SELECT xCol.query('
for $LOC in /locations/location
where $LOC/outcode[.="CM2"]
return
<coordinate>
{ $LOC/x }
{ $LOC/y }
{ $LOC/town }
</coordinate>
') AS Result
FROM [XTable]
/* but as the XQUERY string must be a string literal and not a
string variable, we need to put parameters in via a sql:variable
parameter like this....*/
DECLARE @Postcode VARCHAR(10)
SELECT @Postcode = 'CO8'
SELECT xCol.query('
for $LOC in /locations/location
where $LOC/outcode = sql:variable("@Postcode")
return
<locations>
{ $LOC/whereabouts }
{ $LOC/county }
</locations>
') AS Result
FROM [XTable]
/* Now, this is an open-ended workbench. You have a nice large
source of data, and BOL is now screaming at you to be read. Try
out some FLWOR!
When you tire, it is time to pull in a list of british pubs. */
DECLARE @xmlPubs XML
SELECT @xmlPubs = BulkColumn
FROM OPENROWSET(BULK 'C:\workbench\pubs.xml', SINGLE_BLOB) AS x
CREATE TABLE dbo.Pub
(
Pub_ID INT IDENTITY(1, 1)
NOT NULL,
[Name] VARCHAR(30) NOT NULL,
Address VARCHAR(100) NOT NULL,
outcode VARCHAR(4) NOT NULL,
x INT NULL,
y INT NULL
)
ON [PRIMARY]
INSERT INTO Pub
(
[name],
address,
outcode
)
SELECT x.pub.value('name[1]', 'varchar(30)'),
x.pub.value('address[1]', 'varchar(100)'),
RTRIM(LEFT(
SUBSTRING(x.pub.value('postcode[1]', 'varchar(10)'),
1,
CHARINDEX(' ',
x.pub.value('postcode[1]',
'varchar(10)')
+ ' ', 1) - 1), 4
))
FROM @xmlPubs.nodes('//pubs/pub') AS x ( pub )
UPDATE pub
SET x = f.x, y = f.y
FROM pub
INNER JOIN location f ON pub.outcode = f.outcode
CREATE PROCEDURE spNearestPubs @Postcode VARCHAR(10)
/*
spNearestPubs 'co10'
*/
AS
DECLARE @x INT,
@y INT
SELECT TOP 1--find out our coordinates
@x = x,
@y = y
FROM location
WHERE outcode LIKE RTRIM(LEFT(SUBSTRING(@Postcode, 1,
CHARINDEX(' ', @Postcode + ' ',
1) - 1), 4))
IF @@Rowcount = 0 --typo!
BEGIN
RAISERROR ( 'I don''t recognise the postcode ''%s''', 16, 1,
@postcode )
RETURN 1
END
SELECT TOP 100--list the 100 nearest locations
name + ' ' + address,
[miles] = ROUND(
SQRT(SQUARE(X - @X) + SQUARE(Y - @Y))
* 0.0006214,0)
FROM pub
WHERE x IS NOT NULL
ORDER BY miles
GO
/*
Assigning the result of a SQL query to an XML variable
------------------------------------------------------
well, nice as far as it goes, but why not pass the result back as
an XML variable, and we'll then we can save it direct to disk, or
send it happily to an application, store it in a table as a variable?
XML could be quite handy!
*/
CREATE PROCEDURE spNearestPubsXML
@Postcode VARCHAR(10),
@XMLPubList XML OUTPUT
/*
e.g.
Declare @PubList xml
execute spNearestPubsXML 'co10', @XMLPubList=@PubList output
Select @PubList
*/
AS
DECLARE @x INT,
@y INT
SELECT TOP 1--find out our coordinates
@x = x,
@y = y
FROM location
WHERE outcode LIKE RTRIM(LEFT(SUBSTRING(@Postcode, 1,
CHARINDEX(' ', @Postcode + ' ',
1) - 1), 4))
IF @@Rowcount = 0 --typo!
BEGIN
RAISERROR ( 'I don''t recognise the postcode ''%s''', 16, 1,
@postcode )
SET @XMLPubList = '<pubs />'
RETURN 1
END
SET @XMLPubList = ( SELECT TOP 100--list the 100 nearest locations
[name] = name + ', ' + address,
[miles] = CONVERT(INT,
ROUND(SQRT(
SQUARE(X - @X)
+ SQUARE(Y - @Y))
* 0.0006214, 0))
FROM pub
WHERE x IS NOT NULL
ORDER BY miles
FOR
XML PATH('pub'),
ROOT('pubs'),
TYPE
)
GO
--we can then save the results to disk very easily
DECLARE @PubList XML
EXECUTE spNearestPubsXML 'BR2', @XMLPubList = @PubList OUTPUT
-- We Store the contents of an XML variable to a table
CREATE TABLE xNearestPubs
(
xPubs_ID INT IDENTITY
PRIMARY KEY,
xCol XML
) ;
INSERT INTO xNearestPubs ( xCol )
SELECT @PubList
/*
We Save an XML value to a file.
*/
DECLARE @Command VARCHAR(255)
DECLARE @Filename VARCHAR(100)
SELECT @Filename = 'C:\workbench\Nearestpubs.xml'
/* we then insert a row into the table from the XML variable */
/* so we can then write it out via BCP! */
SELECT @Command = 'bcp "select xCol from ' + DB_NAME()
+ '..xNearestPubs" queryout '
+ @Filename + ' -w -T -S' + @@servername
EXECUTE master..xp_cmdshell @command
--so now the xml is written out to a file
/*
So there we have it. Hopefully, if you enjoyed this approach to XML by
example, we'll try out more complex examples in further Workbenches.
In the meantime, there are other resources on the Simple-Talk ;site ...;
Beginning SQL Server 2005 XML Programming
Srinivas Sampath 21 February 2006
XML has been used to represent semi-structured (as well as unstructured) data such as documents and emails. If information in these models has to be queried, then XML is probably the simplest way to represent such information. Read more...
Understanding XML web services for testers
Helen Joyce - 13 April 2003
This White Paper investigates how XML web services are implemented, considers the customizable features of web services and looks at load testing a web service, specifically so that test strategies can be formulated. Read more...
XML and RDBMS: 10 years on
Jim Fuller - 25 August 2006
As we approach the 10-year anniversary of XML Jim Fuller provides a personal retrospective, focussing on how XML has been and will be used with the RDBMS. Read more...
SQL Server XML Cribsheet
Robyn Page - 29 March 2007
If you find XML a bit of an acronym minefield, Robyn's Cribsheet will help sort out your XSLT from your XDM. Read more...
and we would also
recommend you to read Jacob Sebastian's excellent articles....
...on SQL Server Central
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Author profile: Robyn Page and Phil Factor
Robyn Page is a consultant with Enformatica and USP Networks. She is also a well known actress, being most famous for her role as Katie Williams, barmaid in the Television Series Family Affairs.
Phil Factor (real name withheld to protect the guilty), aka Database Mole, has 20 years of experience with database-intensive applications. Despite having once been shouted at by a furious Bill Gates at an exhibition in the early 1980s, he has remained resolutely anonymous throughout his career.
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