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).