Question

I have a table with an XML type column. This column contains a dynamic list of attributes that may be different between records.

I am trying to GROUP BY COUNT over these attributes without having to go through the table separately for each attribute.

For example, one record could have attributes A, B and C and the other would have B, C, D then, when I do the GROUP BY COUNT I would get A = 1, B = 2, C = 2 and D = 1.

Is there any straightforward way to do this?

EDIT in reply to Andrew’s answer:

Because my knowledge of this construct is superficial at best I had to fiddle with it to get it to do what I want. In my actual code I needed to group by the TimeRange, as well as only select some attributes depending on their name. I am pasting the actual query below:

WITH attributes AS (
  SELECT 
  Timestamp,
  N.a.value('@name[1]', 'nvarchar(max)') AS AttributeName,
  N.a.value('(.)[1]', 'nvarchar(max)') AS AttributeValue  
  FROM MyTable
  CROSS APPLY AttributesXml.nodes('/Attributes/Attribute') AS N(a)
)
SELECT Datepart(dy, Timestamp), AttributeValue, COUNT(AttributeValue)
FROM attributes
WHERE AttributeName IN ('AttributeA', 'AttributeB')
GROUP BY Datepart(dy, Timestamp), AttributeValue

As a side-note: Is there any way to reduce this further?

Answer 1

WITH attributes AS (
  SELECT a.value('(.)[1]', 'nvarchar(max)') AS attribute
  FROM YourTable
  CROSS APPLY YourXMLColumn.nodes('//path/to/attributes') AS N(a)
)
SELECT attribute, COUNT(attribute)
FROM attributes
GROUP BY attribute

CROSS APPLY is like being able to JOIN the xml as a table. The WITH is needed because you can’t have xml methods in a group clause.