hubungan orang tua anak

apakah kueri ini yang Anda cari?

$query =<<<MYSQL
 SELECT `prod_id`
 FROM `produdct_category` 
  INNER JOIN `category` ON `product_category`.`cat_id` = `category`.`id`
 WHERE `category`.`parent_id` = {$selectedParentId}
MYSQL;

Pertanyaan yang diperbarui, jawaban yang diperbarui:

$query =<<<MYSQL
 SELECT *
 FROM `produdcts` 
  INNER JOIN `produdct_category` ON `products`.`prod_id` = `produdct_category`.`prod_id`
  INNER JOIN `category` ON `product_category`.`cat_id` = `category`.`id`
 WHERE `category`.`id` = {$selectedCatId}
   OR `category`.`parent_id` = {$selectedCatId}
MYSQL;