How to select items on table based on 3 relations? - mysql

Question

I have 3 tables:
Categories
| id | name
| 1 | Samsung
| 2 | Apple
Products
| id | category_id | name
| 1 | 1 | Galaxy S4
| 2 | 1 | Galaxy S3
| 3 | 1 | SHG-G600
| 4 | 3 | Lumia 920
Tags
| id | product_id | name | type
| 1 | 1 | smart-phone | phoneType
| 2 | 2 | smart-phone | phoneType
| 3 | 3 | normal-cell | phoneType
| 4 | 1 | red | phoneColor
I'm trying to find a way to select all Samsung devices which have 'smart-phone' as 'phoneType' and 'red' as 'phoneColor'.
So this what I did until now:
SELECT *
FROM `products`
INNER JOIN `product_tag` ON `product_tag`.`product_id` = `products`.`id`
INNER JOIN `tags` ON `tags`.`id` = `products`.`id`
WHERE (
`tags`.`type` = 'phoneType'
AND `tags`.`name` = 'smart-phone'
)
OR (
`tags`.`type` = 'phoneColor'
AND `tags`.`name` = 'red'
)
)
This did not work as is (without selecting category).
I also didn't know how to join categories and add where categories.id = 1.

Answer 1

You can do this by putting the logic in the having clause. For your example code:
SELECT p.*
FROM `products` p join
`product_tag` pt
ON pt.`product_id` = p.`id` join
`tags` t
ON t.`id` = p.`id`
group by p.id
having sum(t.`type` = 'caseMaterial' AND t.name = 'leather') > 0 and
sum(t.`type` = 'caseFor' AND t.`name` = 'iphone-5') > 0;
However, I'm not quite sure how this relates to the tables at the beginning of the question. Your code sample and data layout are not consistent.

Answer 2

I extended the solution of #Gordon Linoff by adding the category join.
SELECT p.*
FROM `products` p join
`categories` c
ON c.`id` = p.`category_id` join
`product_tag` pt
ON pt.`product_id` = p.`id` join
`tags` t
ON t.`id` = pt.`tag_id`
where c.id = 1
group by p.id
having sum(t.`type` = 'phoneType' AND t.name = 'smart-phone') > 0 and
sum(t.`type` = 'phoneColor' AND t.`name` = 'red') > 0
This is working now. Thanks to #Gordon Linoff.