Getting a max value from a node of XML in SQL Server 2008

Question

I have some xml like this

<variable>
  <historicDates>
    <item>
      <date>2012/01/13</date>
      <type>submitted</type>
    </item>
    <item>
      <date>2012/01/12</date>
      <type>required</type>
    </item>
    <item>
      <date>2012/01/11</date>
      <type>required</type>
    </item>
  </historicDates>
</variable>

I am trying to write a sql statement to get the maximum date where the type equals required. To compound the issue I the column is a nvarchar(max) so I know I have to cast it as xml even before I start.

I've tried to figure out the cross apply but cannot get it to work. Any help would be appreciated.

Answer 1

Assuming your XML is in a variable named @xml :

SELECT MAX(t.ItemDate)
    FROM (SELECT Tbl.Col.value('date[1]', 'datetime') AS ItemDate,  
                 Tbl.Col.value('type[1]', 'varchar(20)') AS ItemType 
              FROM @xml.nodes('//variable/historicDates/item') Tbl(Col)) t
    WHERE t.ItemType = 'required'

Since you indicated SQL Server 2008, you could also use a CTE here:

WITH cteXMLtoTable AS (
    SELECT Tbl.Col.value('date[1]', 'datetime') as ItemDate,  
           Tbl.Col.value('type[1]', 'varchar(20)') as ItemType 
        FROM @xml.nodes('//variable/historicDates/item') Tbl(Col)
)
SELECT MAX(ItemDate)
    FROM cteXMLtoTable
    WHERE ItemType = 'required'