Question

I have a table structure as follows and I want to select
all active categories
with active products
of a particular parent ID.

So if I plug in a particular parentID, I only get relevant active subcategories of the parent that contains active products.

This is my sql (mysql) so far which works, but looks pretty nasty, and for the sake of academia I want to know if there’s a better way. It would seem to me that selecting all of the productIDs that are active to filter the results is kind of a waste, but I can’t figure a way around this, or does mysql figure out the best way to process this query?

(many-to-many upon itself)
categories
----------
categoryID
parentID
name
isActive (bool)

(linker table between categories and product)
productCategories
-----------------
productID
categoryID

products
--------
productID
name
isActive (bool)


SELECT productCategories.categoryID, categories.* FROM productCategories
                LEFT JOIN categories ON
                    productCategories.categoryID = categories.categoryID
                WHERE 
                    productCategories.categoryID IN 
                    (SELECT categoryID FROM categories WHERE parentID = {$parentID} AND isActive = 1)
                    AND
                    productCategories.productID IN
                    (SELECT productID FROM products WHERE isActive = 1)
                GROUP BY productCategories.categoryID

Answer 1

An alternative layout could be as follows…

SELECT
  *
FROM
(
  SELECT
    productCategories.categoryID
  FROM
    productCategories
  INNER JOIN
    categories
      ON categories.categoryID = productCategories.parentID
  INNER JOIN
    products
      ON products.productID    = productCategories.productID
  WHERE 
    categories.parentID = {$parentID}
    AND categories.isActive = 1
    AND products.isActive = 1
  GROUP BY
    productCategories.categoryID
)
  AS category_map
LEFT JOIN
  categories AS [children]
    ON category_map.categoryID = categories.categoryID