SQL Server 2012 : Using XML Data - XQuery and FLWOR Operations

2/10/2014 12:40:44 AM

XQuery is a language that provides the ability to query structured and semi-structured XML data. XQuery is based on the existing XPath query language but includes added support for improved iteration, sorting results, and XML construction.

The real muscle of XQuery comes with the FLWOR operation. FLWOR stands for FOR LET WHERE ORDER BY and RETURN.

The following example is an example of a basic FLWOR query using for and return:

DECLARE @var xml
SET @var = ‘
<Item>
    <ItemNumber>V001</ItemNumber>
    <ItemNumber>A017</ItemNumber>
</Item>
'

SELECT @var.query('for $item in Item/ItemNumber return $item')

/*
<ItemNumber>V001</ItemNumber>
<ItemNumber>A017</ItemNumber>
*/

where and order by can be specified to filter and sort the output:

DECLARE @var xml
SET @var = ‘
<Item>
    <ItemNumber>1010</ItemNumber>
    <ItemNumber>1009</ItemNumber>
    <ItemNumber>1008</ItemNumber>
    <ItemNumber>1007</ItemNumber>
    <ItemNumber>1006</ItemNumber>
    <ItemNumber>1005</ItemNumber>
    <ItemNumber>1004</ItemNumber>
    <ItemNumber>1003</ItemNumber>
    <ItemNumber>1002</ItemNumber>
    <ItemNumber>1001</ItemNumber>
</Item>
'

SELECT @var.query('
    for $item in Item/ItemNumber 
    where $item[.>"1005"]
    order by $item
    return $item')

<ItemNumber>1006</ItemNumber>
<ItemNumber>1007</ItemNumber>
<ItemNumber>1008</ItemNumber>
<ItemNumber>1009</ItemNumber>
<ItemNumber>1010</ItemNumber>

The where clause filters the XQuery expression for item numbers greater than 1005, and the order by clause orders the nodes in ascending order.

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