How can I split a mysql table into multiple tables and query the correct arrea?

Question

Below is my friend table,
I included 2 entries to show how it works, When a user adds a person as a friend it inserts 2 entries into the DB with this code;

<?PHP

 //status 0=approved 1=declined approval 3=pending approval
$sql = "insert into friend_friend (userid,friendid,status,submit_date) 
    values
    ('$_SESSION[auto_id]','$friendid','0',now()), 
    ('$friendid','$_SESSION[auto_id]','3',now())"; //Line above is my user ID, the other users ID, status 0 for approved on my side, date
                //next entry is the receiving users entry, there ID, my ID, 3 for not approved yet, date
executeQuery($sql);

//So that code above is my php that adds a friend

//Below is my table scheme for the friends table
CREATE TABLE IF NOT EXISTS `friend_friend` (
  `autoid` int(11) NOT NULL AUTO_INCREMENT,
  `userid` int(10) DEFAULT NULL,
  `friendid` int(10) DEFAULT NULL,
  `status` enum('1','0','3') NOT NULL DEFAULT '0',
  `submit_date` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `alert_message` enum('yes','no') NOT NULL DEFAULT 'yes',
  PRIMARY KEY (`autoid`),
  KEY `userid` (`userid`),
  KEY `friendid` (`friendid`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1756421 ;

--
-- Dumping data for table `friend_friend`
--
INSERT INTO `friend_friend` (`autoid`, `userid`, `friendid`, `status`, `submit_date`, `alert_message`) VALUES
(637229, 2, 1, '1', '2007-10-18 01:02:00', 'no');
INSERT INTO `friend_friend` (`autoid`, `userid`, `friendid`, `status`, `submit_date`, `alert_message`) VALUES
(637230, 1, 2, '1', '2007-10-18 01:02:00', 'no');

INSERT INTO `friend_friend` (`autoid`, `userid`, `friendid`, `status`, `submit_date`, `alert_message`) VALUES
(637231, 22901, 1, '1', '2007-10-18 02:24:05', 'no');
INSERT INTO `friend_friend` (`autoid`, `userid`, `friendid`, `status`, `submit_date`, `alert_message`) VALUES
(637232, 1, 22901, '1', '2007-10-18 02:24:05', 'no');
?>

What I am wanting to do is split the friend_friend table up into multiple tables based on user ID number
Like all user ID's between 1-20,000 go to one table, all userIDs 20,001-40,000, 40,001-60,000 all go to a different table

I am not sure how to do this best, I would need to detect which table a user should query when adding a new friend and well as when retrieving friend list of users
I assume in my code at the top, the 2 entries to add a user would have to be broken into 2 queries and update different tables probably?

Answer 1

Assuming you are using MySQL 5.1 or above, then you can use partitioning to do what you want. See the following links:

http://dev.mysql.com/doc/refman/5.1/en/partitioning.html

http://dev.mysql.com/tech-resources/articles/performance-partitioning.html

Answer 2

The term of art is "sharding" (to help you in literature searches, web searches, etc) -- or at least, one popular term of art (vocabulary is unfortunately not fully settled in this area). Once you do research it you'll learn that the concomitant problem is having to query all shards (and UNION ALL them, typically -- or sometimes aggregate them back in different ways) when you don't know where (part or all of) the answer(s) may be.

So, sharding (in particular "horizontal sharding", which is what you're doing here) should be done advisedly in application-specific ways, to try and group entries that are "together" so that as often as feasible checking a single shard will suffice. Vertical sharding (putting different columns, rather than rows, in different tables) is easier to design, as you need only examine the most frequent queries to ensure each of them can be entirely satisfied by very few (ideally only one) shard.

Oh, and, of course, this huge amount of delicate, advanced work is NOT really worth doing until it does get proven to be needed -- and then, it will be to ensure the database backend's work is split among many servers, because a single server just can't cut it any longer. You appear to be just trying to learn the very fundamentals of sharding (my apologies if I'm reading this wrong!-) and part of the problem -- like for other hard and important parts of system architecture -- is that there's no real motivation until the system size goes WELL above what's reasonable to present in a "toy application"...!-)