How to store/query users meta-data by zip code - mysql

Question

I have a complicated issue but rather than go into the specifics i have simplified it to the following.
Lets say we are trying to build a system, where users of the system can apply for priority levels on various services on a per zip-code basis. This system would have four tables like so...
CREATE TABLE `zip_code` (
`zip` varchar(7) NOT NULL DEFAULT '',
`lat` float NOT NULL DEFAULT '0',
`long` float NOT NULL DEFAULT '0'
PRIMARY KEY (`zip`,`lat`,`long`),
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
CREATE TABLE `user` (
`user_id` int(10) NOT NULL AUTO_INCREMENT
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
CREATE TABLE `service` (
`service_id` int(10) NOT NULL AUTO_INCREMENT
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
CREATE TABLE `service_priority` (
`user_id` int(10) NOT NULL',
`service_id` int(10) NOT NULL',
`zip` varchar(7) NOT NULL,
`priority` tinyint(1) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
Now lets also say that we have 45000 zip-codes, a few hundred services and a few thousand users, and that no user can have the same priority level as another user for the same service in the same zip code.
I need a query that if given a particular zip code, radius, service, and a user_id will return the highest available priority level for all other zip codes within that radius for that service.
And, also, would like to know any suggestions for restructuring this data.
The problem that i see happening here is as the user base grows, the service_priority table is going to get huge, in theory 45000 rows bigger for every user although in practice probably only 10000 rows bigger.
What can i do to mitigate these problems?

Answer 1

Switch to InnoDB.
zip_code table should probably have PRIMARY KEY(zip) unless you really want multiple rows for a given zip.
"no user can have the same priority level as another user for the same service in the same zip code" -- can be enforced by
service_priority : UNIQUE(service_id, user_id, zip)
Then your query may look something like
SELECT sp.*
FROM ( SELECT b.zip
FROM ( SELECT lat, lng FROM zip_code WHERE zip = '$zip' ) AS a
JOIN zip_code AS b
WHERE ... < $radius
) AS z
JOIN service_priority AS sp
WHERE sp.zip = z.zip
AND sp.user_id = $user_id
AND sp.service_id = $service_id
ORDER BY sp.priority DESC
LIMIT 1
Notes:
The index, above, is also tailored for this query.
The innermost query gets the one lat/lng for the center point.
The middle query focuses on finding the nearby zips. See the tag I added to find many questions discussion how to do that.
The outer query then filters results based on user and service.
Finally, the highest priority row is picked.