mysql error in my query - mysql

Question

i have to check in my products i am selling (mostly gaming consoles and games)
i want to see which products has which categories and this is my query:
select * From products left join products_categories on (product_id=id) ;
+------+------+------------+-------------+----------
| id | name | product_id | category_id | and more
+------+------+------------+-------------+----------
| 4 | Xbox | 4 | 2 |
| 5 | PS3 | 5 | 2 |
| 7 | BAD | NULL | NULL |
etc...
+------+------+------------+-------------+---------
here i have a product (#7 - BAD) that i don'T want to see since i removed the category,
I don't want to see the product without categories?

Answer 1

The LEFT JOIN command is used to combines null matching rows which are
stored in related tables In order to join these tables, the join table
require a common field (commonly called foreign key) from the left
table. This type of join requires keywords ON or USING.
Example:
SELECT *
From products
LEFT JOIN products_categories ON (product_id=id)
WHERE product_id IS NOT NULL;
Or you can use the INNER JOIN:
The JOIN or INNER JOIN command is used to combines non-null matching
rows which are stored in related tables In order to join these tables,
the join table require a common field (commonly called foreign key)
from the left table. This type of join requires keywords ON or USING.
Example:
SELECT * From products INNER JOIN products_categories ON (product_id=id);
Now, I would recommend to add a flag for inactive or active product, this way you don't need to remove the categories for a product if it's inactive. This way, if you want to re-activate it, simply turn the flag back to 1 or whatever flag you use.
Example:
SELECT *
FROM products
INNER JOIN products_categories ON (product_id=id)
WHERE products.is_active = 1;