MySQL Database design advice - using joins - mysql

Question

I am building an AJAX like search page which allows a customer to select a number filters that will narrow down the search. For instance, a user has selected an 'iPhone 5' and has additional filters for capacity (32GB, 64GB) & colour (black, white..).
The user can only select a single radio box per category (so they could select 32GB & Black).. but they could not select (32GB & 64GB & black as two of these belong to the 'capacity' category).
I have added the schema here on sqlfiddle (please ignore the fact i've removed the primary keys they exist in the proper app they have just been removed along with some other fields/data to minimise the sqlfiddle)
http://sqlfiddle.com/#!2/964425
Can anyone suggest the best way to create the query to do the following:
Get all the prices for device_id '2939' (iPhone 5) which has the 'attributes' of '32GB' AND 'Black'
I currently have this - but this only works when selecting for a single attribute:
// search for device with '64GB' & 'Black' attributes (this currently doesn't return any rows)
SELECT `prices`.*
FROM (`prices`)
LEFT JOIN `prices_attributes` ON `prices_attributes`.`price_id` = `prices`.`id`
WHERE `prices`.`device_id` = '2939'
AND `attribute_option_id` = '19'
AND `attribute_option_id` = '47';
// search for device with '64GB' attribute only (this currently DOES return a row)
SELECT `prices`.*
FROM (`prices`)
LEFT JOIN `prices_attributes` ON `prices_attributes`.`price_id` = `prices`.`id`
WHERE `prices`.`device_id` = '2939'
AND `attribute_option_id` = '19';
Any advice on the database design would be appreciated too
Note: I was thinking to have a new column within the 'prices' table that has the matching attribute_ids serialised - would this be not good for optimisation however (e.g would it be slower than the current method)

Answer 1

Since attribute_option_id is an atomic value, it cannot have two different values for the same row. So your WHERE clause cannot match any record:
SELECT `prices`.*
FROM (`prices`)
LEFT JOIN `prices_attributes` ON `prices_attributes`.`price_id` = `prices`.`id`
WHERE `prices`.`device_id` = '2939'
AND `attribute_option_id` = '19' # Here for one row, attribute_option_id is either 19
AND `attribute_option_id` = '47'; # of '47'. Cannot be the both
Instead of JOIN, you could try a subquery if you feel that is more readable. I think MySQL allow that syntax:
SELECT `prices`.*
FROM `prices`
WHERE `prices`.`device_id` = '2939'
AND EXISTS (SELECT *
FROM prices_attributes
WHERE price_id = `prices`.`id`
AND attribute_option_id IN ('19', '47') )
I don't know how MySQL will optimize the above solution. An alternative would be:
SELECT `prices`.*
FROM `prices`
WHERE `prices`.`id` IN (
SELECT DISTINCT `price_id`
FROM prices_attributes
WHERE attribute_option_id IN ('19', '47')
)

Answer 2

I think you should use the IN operator for the attribute_option_id and you set the values dynamically to the query; Also, using group_by you have only one row per price so in effect you get all the prices. Apart from this, the design is ok.
Here, I have made an example:
SELECT `prices`.*
FROM (`prices`)
LEFT JOIN `prices_attributes` ON `prices_attributes`.`price_id` = `prices`.`id`
WHERE `prices`.`device_id` = '2939'
and `attribute_option_id` in ('19','47')
group by `prices`.`device_id`, `prices`.`price`;
Here, you can also add an order clause to order by price:
order by `prices`.`price` desc;
Another way to solve this would be to use a distinct on price, like this:
select distinct(prices.price)
from prices
where prices.device_id = 2939
and id in (select price_id from prices_attributes where attribute_option_id in (19,47));

Answer 3

Join against the devices_attributes_options table several times, once for each attribute the item must have
Something like this:-
SELECT *
FROM devices a
INNER JOIN prices b ON a.id = b.device_id
INNER JOIN prices_attributes c ON b.id = c.price_id
INNER JOIN devices_attributes_options d ON c.attribute_option_id = d.id AND d.attribute_value = '32GB'
INNER JOIN devices_attributes_options e ON c.attribute_option_id = e.id AND e.attribute_value = 'Black'
WHERE a.id = 2939
As to putting serialised details into a field, this is a really bad idea and would come back to bite you in the future!

Answer 4

SELECT * FROM prices WHERE device_id=2939 AND id IN (SELECT price_id FROM prices_attributes WHERE attribute_option_id IN (19,47));
Is it what you're looking for?
EDIT: sorry, didn't notice you're asking for query using joins