select element frequency over xml column

Question

Consider this table structure in Sql Server:

ID - uniqueidentifier
Params - xml

and rows in following format:

<!--ROW1 xml column content-->
<Params>
  <Module>
    <ModuleName>Module1</ModuleName>
  </Module>
  <Module>
    <ModuleName>Module2</ModuleName>
  </Module>
</Params>

<!--ROW2 xml column content-->
<Params>
    <Module>
        <ModuleName>Module1</ModuleName>
    </Module>
</Params>

Expected output (the sum of all occurrences of each element across the table):

_______________
| Module1 | 2 |
| Module2 | 1 |
|_____________|

Count of elements Module is 0..n in each row. I was trying to create stored procedure which returns multiple rows for each xml field input and then contribute results from each row into temp table but I had not luck with finding correct syntax. Can somebody refer to relevant resource or show some little snippet how to deal with it? Thanks for any hint provided.

Answer 1

You can apply some xquery to grab the Module Names and then count them with a GROUP BY:

SELECT ModuleName, COUNT(*) AS NumOccurrences
FROM
(
   SELECT
     Nodes.node.value('(ModuleName)[1]', 'varchar(50)') AS ModuleName
   FROM
       Modules m
       cross apply m.Params.nodes('//Module') as Nodes(node)
) x
GROUP BY ModuleName;

(Unfortunately, we can't group directly on xml, hence the need for the derived table)

SqlFiddle here

Answer 2

Further to Stuart's answer, you can use the over clause

select distinct 
       t.x.value('.','varchar(50)'), 
       COUNT(*) over (partition by t.x.value('.','varchar(50)'))  
from yourtable 
    cross apply x.nodes('/Params/Module/ModuleName') t(x)