MYSQL-SELECT产品的parent_category处于活动状态

Question

assuming we have a database category structure like this

# Categories Table
| category_id | parent_category_id | status |

# Products Table
| product_id | category_id |

how do i get the list of products in a category only if the parent_category_id has an active status = 1 ?

i guess i could use some sub-query in the SELECT statement, but i don't know how! :(

something like:

SELECT p.*, (SELECT * FROM ? WHERE ? ) AS x 
FROM products AS p 
    LEFT JOIN categories AS c ON p.category_id = c.category_id 
WHERE ... 
AND p.product_id = '?' 
AND ...

Thank you in advance for any advice!

NB: i'm using PHP as backend language, just in case i need some sort of data manipulation to pass to the mysql query.

Answer 1

try not to use subquery, because it can affect the speed of loading data

maybe it can help

SELECT *
FROM categories c
INNER JOIN products p ON p.category_id=c.category_id
WHERE c.status = 1

Answer 2

SELECT p.* FROM products p
INNER JOIN categories child ON child.category_id = p.category_id
INNER JOIN categories parent ON parent.category_id = child.parent_category_id
WHERE parent.status=1

Answer 3

Here a example query, I don't use left join or join, becasue you require that the record exists in order to get the status.

SELECT 
   *
FROM
   products, categories
WHERE
   products.category_id = categories.category_id
   AND status = '1'

Answer 4

First you have to get all active categories

SELECT child.*
FROM Categories child
JOIN Categories parent
  ON child.parent_category_id = parent.category_id 
 AND parent.status = 1

But you also need the root categories with not parent_id

SELECT *
FROM Categories
WHERE parent_category_id IS NULL
  AND status = 1

So you UNION both

SELECT *
FROM Categories child
JOIN Categories parent
  ON child.parent_category_id = parent.category_id 
 AND parent.status = 1

UNION ALL

SELECT *
FROM Categories
WHERE parent_category_id IS NULL
  AND status = 1

Now you get the products for those categories

SELECT *
FROM (  ... UNION ALL ... ) active_categories
JOIN Products
 ON active_categories.category_id = Product.category_id