Question

I am getting the following error:

1052 – Column ‘product_id’ in field list is ambiguous

When I run the following:

SELECT `product_id`, `product_name`
FROM `products`
INNER JOIN `products_has_product_category`
   ON `products.product_id` = `products_has_product_category.product_id`
   AND `products_has_product_category.category_id` = 1
ORDER BY `products.product_name`

My PRODUCTS table has

product_id, product_name, etc 

My products_has_product_category table has

product_id, category_id

This is my first try at a join, so I appreciate the help!

Answer 1

You need to specify which table the product_id comes from. Since the product_id is in both tables, when you SELECT it you need to specify which table you want the value from. With a table alias:

SELECT p.product_id, p.product_name
FROM `products` p
INNER JOIN `products_has_product_category` pc
    ON p.product_id = pc.product_id
    AND pc.category_id = 1
ORDER BY p.product_name

Without table aliases:

SELECT `products`.`product_id`, `products`.`product_name`
FROM `products`
INNER JOIN `products_has_product_category`
  ON `products.product_id` = `products_has_product_category.product_id`
  AND `products_has_product_category.category_id` = 1
ORDER BY `products.product_name`