multiple WHERE clauses on a joined table - mysql

Question

I have a simple application that tracks diners and their favorite flavors and desserts. The records table is just the diner's name and ID, the mid table tracks the desserts and flavors (again by an ID linked to another table of values).
CREATE TABLE IF NOT EXISTS `records` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
INSERT INTO `records` (`id`, `name`) VALUES
(1, 'Jimmy Jones'),
(2, 'William Henry');
CREATE TABLE IF NOT EXISTS `mid` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`diner` int(11) NOT NULL,
`dessert` int(11) NOT NULL DEFAULT '0',
`flavor` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=11 ;
INSERT INTO `mid` (`id`, `diner`, `dessert`, `flavor`) VALUES
(1, 1, 3, 0),
(2, 1, 2, 0),
(3, 1, 15, 0),
(4, 1, 0, 1),
(5, 2, 3, 0),
(6, 2, 6, 0),
(7, 2, 0, 4),
(8, 1, 34, 0),
(9, 2, 0, 4),
(10, 2, 0, 22);
I'm a little stumped by what should be a simple query-- I want to get all IDs from the records table where certain dessert or flavor requirements are met:
SELECT a.id
FROM records AS a
JOIN mid AS b ON a.id = b.diner
WHERE b.dessert IN (3,2,6)
AND b.flavor IN (4,22)
This query returns no rows, even though there are records that match the where clauses. I am pretty sure I'm missing something obvious with the JOIN but I've tried INNER, OUTER, LEFT and RIGHT with no success.
Can someone put me on the right track and explain what I'm missing?
Thanks

Answer 1

You seem to want diners that have the combinations. Here is one way:
select diner
from records
group by diner
having max(b.dessert = 3) = 1 and
max(b.dessert = 2) = 1 and
max(b.dessert = 6) = 1 and
max(b.flavor = 4) = 1 and
max(b.flavor = 22) = 1
This answers your comment:
select diner
from records
group by diner
having max(case when b.dessert in (2, 3, 6) then 1 esle 0 end) = 1 and
max(case when b.dessert in (4, 22) then 1 else 0 end) = 1
If you are just looking for the records in a that match the conditions, use:
select r.*, d.name
from records r join
diner d
on r.diner = d.id
where b.dessert IN (3,2,6) AND b.flavor IN (4,22)
If this is what you want, the join condition in your query is wrong (a.id should be a.diner).

Answer 2

You SQL statement is fine, but non of your sample records meet your condition, records that would match should look like this
dessert flavor
3 4
3 22
2 4
2 33
6 4
6 22
Non of your input record has any of these combinations

Answer 3

Your WHERE condition does not fit any record in the "mid" table.
There are no records that have dessert in (3, 2, 6) AND flavor in (4, 22), so the query (correctly)returns no result.

Answer 4

You don't have any records that match both where conditions.
( 1, 1, 3, 0) - Matches dessert IN (3,2,6)
( 2, 1, 2, 0) - Matches dessert IN (3,2,6)
( 3, 1, 15, 0)
( 4, 1, 0, 1)
( 5, 2, 3, 0) - Matches dessert IN (3,2,6)
( 6, 2, 6, 0) - Matches dessert IN (3,2,6)
( 7, 2, 0, 4) - Matches flavor IN (4,22)
( 8, 1, 34, 0)
( 9, 2, 0, 4) - Matches flavor IN (4,22)
(10, 2, 0, 22) - Matches flavor IN (4,22)
Perhaps you meant OR?
SELECT a.id
FROM records AS a
JOIN mid AS b ON a.id = b.diner
WHERE b.dessert IN (3,2,6)
OR b.flavor IN (4,22)
Should return 7 results.
Also, your thoughts on JOIN are a red herring. The difference between LEFT and RIGHT is just which table gets precedence when the join clause doesn't match records between them. The difference between INNER and OUTER is just what happens when there isn't a matching record between the two tables. Try this explanative article from coding horror for more details on joins (helpfully pointed out to me in a different SO question, heh).