Archive for the ‘XQuery’ Category
SQL Server XQuery
I promised my students an example of writing xquery statements in Microsoft SQL Server. This post builds on two earlier posts. The first qualifies how to build a marvel
table with source data, and the second qualifies how you can create an XML Schema Collection and insert relational data into an XML structure.
You can query a sequence with xquery as follows:
DECLARE @x xml; SET @x = N''; SELECT @x.query('(1,2,(10,11,12,13,14,15)),-6'); |
It returns:
1 2 10 11 12 13 14 15 -6 |
You can query a sequence with an xquery FLOWR
statement. FLOWR
stands for: FOR
, LET
, ORDER BY
, WHERE
, and RETURN
. A sample xquery with a FLOWER
statement is:
DECLARE @x xml; SET @x = N''; SELECT @x.query('for $i in ((1,2,(10,11,12,13,14,15)),-6) order by $i return $i'); |
It returns:
-6 1 2 10 11 12 13 14 15 |
You can query the entire node tree with the following xquery statement because it looks for the occurrence of any node with the /*
search string:
DECLARE @x xml; SET @x = N'<marvel> <avenger_name>Captain America</avenger_name> </marvel>'; SELECT @x.query('/*'); |
You can query the avenger_name
elements from the marvel_xml
table with the following syntax:
SELECT xml_table.query('/marvel/avenger_name') FROM marvel_xml; |
It returns the following set of avenger_name
elements:
<avenger_name>Hulk</avenger_name> <avenger_name>Iron Man</avenger_name> <avenger_name>Black Widow</avenger_name> <avenger_name>Thor</avenger_name> <avenger_name>Captain America</avenger_name> <avenger_name>Hawkeye</avenger_name> <avenger_name>Winter Soldier</avenger_name> <avenger_name>Iron Patriot</avenger_name> |
You can query the fourth avenger_name
element from the marvel_xml
table with the following xquery statement:
SELECT xml_table.query('/marvel[4]/avenger_name') FROM marvel_xml; |
It returns the following avenger_name
element:
<avenger_name>Thor</avenger_name> |
You can use the value()
function to verify an avenger_name
element exists:
SELECT CASE WHEN xml_table.value('(/marvel[4]/avenger_name)','nvarchar') = 'T' THEN 'Exists' END AS "Verified" FROM marvel_xml WHERE id = 3; |
The query returns the Exists
string when it finds a valid avenger_name
element. You have a number of other tools to query results sets from the XML node tree.
I hope this helps my students and anybody interested in writing xquery-enable queries.
MarkLogic Install & Config
My data warehousing class goes through traditional design methods, like Kimball. Then, we explore XML databases. We use the Community License of the MarkLogic 4.2 Server, which is the engine of O’Reilly’s Safari online.
You can find the installation, configuration, and client-tool installation/configuration of the MarkLogic Server in the following blog pages:
- Installation, License, and first-use configuration
- Configuration of a Forest, HTTP Server, and WebDAV
- CQ client software
You can find the list of potential function here on the developer’s site for MarkLogic.
Quick XML update
Somebody commented last week that they’d like the source code for an XSL example file found in this older post. I’ve added the requested code there. The code lets you query directly from your XSL against an Oracle database.
I’ve also created a top page for collecting references to XML blog pages and posts. It’s only got a few but it is an area that will be expanded.