Types don't match between the anchor and the recursive part in column of recursive query

Question

Given a category @categoryId, the query should recursively navigate to the top most super-category, which has been accomplished.

Now I'd like also to generate all along a string which would be the concatenation of all the CategoryName in the process.

DECLARE @CategoryId AS int = 217;
WITH Categories AS
(
   SELECT ParentCategoryId, CategoryName, '' AS strCategory
   FROM Category 
   WHERE CategoryId = @CategoryId

   UNION ALL

   SELECT c.ParentCategoryId, c.CategoryName,
       (c.CategoryName + ': ' + cts.strCategory) AS strCategory  
   FROM Category AS c
   JOIN Categories AS cts
   ON c.CategoryId = cts.ParentCategoryId
)

SELECT TOP 1 CategoryName, LEN(CategoryName) AS strLength
FROM Categories
ORDER BY strLength DESC

With the above code I'm getting the following error:

Types don't match between the anchor and the recursive part in column 
"strCategory" of recursive query "Categories".

Thanks for helping

Answer 1

Try changing the query to cast the varchars to VARCHAR(MAX).

Something like

DECLARE @CategoryId AS int = 217;
WITH Categories AS
(
   SELECT ParentCategoryId, CategoryName, CAST('' AS VARCHAR(MAX)) AS strCategory
   FROM Category 
   WHERE CategoryId = @CategoryId

   UNION ALL

   SELECT c.ParentCategoryId, c.CategoryName,
       CAST((c.CategoryName + ': ' + cts.strCategory) AS VARCHAR(MAX)) AS strCategory  
   FROM Category AS c
   JOIN Categories AS cts
   ON c.CategoryId = cts.ParentCategoryId
)

SELECT TOP 1 CategoryName, LEN(CategoryName) AS strLength
FROM Categories
ORDER BY strLength DESC