Question

I have this table for a cardgame with 2-4 players:

CREATE TABLE IF NOT EXISTS `cardgame` (
  `id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
  `players` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `p1` mediumint(6) unsigned NOT NULL DEFAULT '0',
  `p2` mediumint(6) unsigned NOT NULL DEFAULT '0',
  `p3` mediumint(6) unsigned NOT NULL DEFAULT '0',
  `p4` mediumint(6) unsigned NOT NULL DEFAULT '0',
  `p1_state` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `p2_state` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `p3_state` tinyint(1) unsigned NOT NULL DEFAULT '0',
  `p4_state` tinyint(1) unsigned NOT NULL DEFAULT '0',
  /* other rows */,
  `game_state` tinyint(1) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=79218 DEFAULT CHARSET=utf8;

I have to check all games, where I am a player. (my user_id is 1981 in the example)

mysql> EXPLAIN SELECT id FROM cardgame 
WHERE ((p1=1981 AND p1_state=1) OR (p2=1981 AND p2_state=1) 
OR (p3=1981 AND p3_state=1) OR (p4=1981 AND p4_state=1)) 
AND game_state < 7;
+----+-------------+----------+------+---------------+------+---------+------+-------+-------------+
| id | select_type | table    | type | possible_keys | key  | key_len | ref  | rows  | Extra       |
+----+-------------+----------+------+---------------+------+---------+------+-------+-------------+
|  1 | SIMPLE      | cardgame | ALL  | NULL          | NULL | NULL    | NULL | 79208 | Using where |
+----+-------------+----------+------+---------------+------+---------+------+-------+-------------+

On which rows can I create indexes?
the p1, p1_state, p2.. p3.. p4, p4_state rows needs the index plus the game_state, but isn’t it too much?

Or I have to redesign the schema in some way?

Answer 1

Or I have to redesign the schema in some way?

Yes, normalise your schema:

CREATE TABLE game_players (
  game_id  MEDIUMINT NOT NULL,
  position TINYINT   NOT NULL,
  player   MEDIUMINT NOT NULL,
  state    TINYINT UNSIGNED NOT NULL DEFAULT 0,
  PRIMARY KEY (game_id, position),
  UNIQUE (game_id, player), -- if a player can only be in each game once
  INDEX (player, state)
)
SELECT id, 1, p1, p1_state FROM cardgame
  UNION ALL
SELECT id, 2, p2, p2_state FROM cardgame
  UNION ALL
SELECT id, 3, p3, p3_state FROM cardgame
  UNION ALL
SELECT id, 4, p4, p4_state FROM cardgame;

ALTER TABLE cardgame 
  DROP p1, DROP p1_state,
  DROP p2, DROP p2_state,
  DROP p3, DROP p3_state,
  DROP p4, DROP p4_state;

Then your query becomes:

SELECT g.id
FROM   game_players p JOIN cardgame g ON p.game_id = g.id
WHERE  p.player = 1981 AND p.state = 1
   AND g.game_state < 7;