Question

I have the following MYSQL query:

SELECT categories.key, categories.name, count(*) as itemsCount 
    FROM categories 
        LEFT JOIN designs 
            ON categories.key = designs.category 
    GROUP BY categories.name ASC

It does the job of selecting all categories and counting the # of designs that belong to each category. However, my app and the DB are set so that if the “category” field in the “designs” table has a value of “0”, then this design belong to the virtual (there is no category with key = 0 in the “categories” table) “unassigned” category.

My question is… is it possible to modify my query to also count designs that do NOT belong to any of the existing categories?

Perhaps I am over-complicating things and it’s much easier to add a category with a “0” key, but for the sake of learning, perhaps there is a better way?

Thanks.

Answer 1

SELECT  d.category, c.name, COUNT(d.category)
FROM    (
        SELECT  0 AS key, 'VIRTUAL' AS name
        UNION ALL
        SELECT  key, name
        FROM    categories
        ) c
LEFT JOIN
        designs d
ON      d.category = c.key
GROUP BY
        c.key