If the productCategory field contains values such as "042002" then
$query = "select * from storeProduct where productInventory LIKE '%042%' AND productInventory LIKE '%002%' order by productCategory, productName ASC";
If you want to pull records that contain 042 OR 002 then
$query = "select * from storeProduct where productInventory = '042' OR productInventory ='002' order by productCategory, productName ASC";