Getting percentage of “Count(*)” to the number of all items in “GROUP BY”

Question

Let\'s say I need to have the ratio of "number of items available from certain category" to "the number of all items". Please consider a

Answer 1

This should do it:

SELECT I.category AS category, COUNT(*) AS items, COUNT(*) / T.total * 100 AS percent
FROM Item as I,
     (SELECT COUNT(*) AS total FROM Item WHERE Department='Popular') AS T
WHERE Department='Popular'
GROUP BY category;