Dynamic IN+IF clause with GROUP_CONCAT? - mysql

Question

I am filtering buyers (many) for a given property (one) with the main condition of
if the buyer requires specific exact # of bathrooms (buyers.bathroom_exact='1'), match it to the property's bathroom value.
Buyers can select multiple exact bathroom matches. Here's a sample schema:
CREATE TABLE `buyers` (
`id` int(10) NOT NULL AUTO_INCREMENT,
`name` text NOT NULL,
`bathroomreq` tinyint(1) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
CREATE TABLE `buyers_bathrooms` (
`buyer_id` int(10) unsigned NOT NULL DEFAULT '0',
`number` decimal(10,2) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `buyers` ( name, bathroomreq ) VALUES ( 'John Doe', 1);
INSERT INTO `buyers` ( name, bathroomreq ) VALUES ( 'John Smith', 1);
INSERT INTO buyers_bathrooms ( buyer_id, number ) VALUES ( 1, 8 );
INSERT INTO buyers_bathrooms ( buyer_id, number ) VALUES ( 1, 9 );
INSERT INTO buyers_bathrooms ( buyer_id, number ) VALUES ( 1, 10 );
INSERT INTO buyers_bathrooms ( buyer_id, number ) VALUES ( 2, 5 );
The only way I can think of doing this is using a column which has an IF clause to see if the bathroomreq is 1, then match the group_concat of the buyers specified bathrooms:
SELECT IF ( bathroomreq = '1', 8 IN (
SELECT GROUP_CONCAT(number) AS bathrooms
FROM buyers_bathrooms
WHERE buyers.id = buyers_bathrooms.buyer_id
) , 1 ) AS bathroom_match,
bathroomreq,
id, name
FROM buyers
So this property basically has 8 bathrooms and that's why 8 is hardcoded in there.
Here's a mysql fiddle:
http://sqlfiddle.com/#!2/508cc/1
Is this the only way of solving the problem and is it reliable? Can I do it an alternative way with something like a dynamic INNER JOIN if bathroomreq is 1? Basically, can I avoid having to branch based on bathroom_match in my application code and filter this elegantly through SQL alone?

Answer 1

I think you can do what you want with an exists clause:
select b.bathroomreq, b.id, b.name,
(b.bathroomreq <> 1 or
exists (select 1
from buyers_bathrooms bb
where bb.buyer_id = b.id and bb.number = 8
)
) as bathroom_match
from buyers b;