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

SELECT Category, COUNT(*) AS Total , (COUNT(*) / (SELECT COUNT(*) FROM Item WHERE Department='Popular')) * 100 AS 'Percentage to all items', 
FROM Item
WHERE Department='Popular'
GROUP BY Category;

I'm not sure of the MySql syntax, but you can use a sub-query as shown.