MySQL limit 优化方案

准备数据:tudou@gyyx

mysql> show create table tmp\g
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                      |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tmp   | CREATE TABLE `tmp` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `ctime` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `stat` enum('1','0','2') DEFAULT '1',
  PRIMARY KEY (`id`),
  KEY `ix_ics` (`stat`,`ctime`,`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3000001 DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

存储过程:tudou@gyyx

CREATE PROCEDURE `proc_buildata`(IN loop_times INT)
BEGIN  
DECLARE var INT DEFAULT 0;  
WHILE var<loop_times DO  
SET var=var+1;  
INSERT INTO tmp (ctime,stat) VALUES (NOW(),MOD(var,3));  
END WHILE;  
END

执行查询:tudou@gyyx

mysql>  SELECT id FROM tmp WHERE stat=2 ORDER BY ctime LIMIT 900000,20;
+---------+
| id      |
+---------+
| 2700002 |
| 2700005 |
| 2700008 |
| 2700011 |
| 2700014 |
| 2700017 |
| 2700020 |
| 2700023 |
| 2700026 |
| 2700029 |
| 2700032 |
| 2700035 |
| 2700038 |
| 2700041 |
| 2700044 |
| 2700047 |
| 2700050 |
| 2700053 |
| 2700056 |
| 2700059 |
+---------+
20 rows in set (0.38 sec)

执行计划:tudou@gyyx

mysql> EXPLAIN SELECT id FROM tmp WHERE stat=2 ORDER BY ctime LIMIT 900000,20;
+----+-------------+-------+------+---------------+--------+---------+-------+---------+--------------------------+
| id | select_type | table | type | possible_keys | key    | key_len | ref   | rows    | Extra                    |
+----+-------------+-------+------+---------------+--------+---------+-------+---------+--------------------------+
|  1 | SIMPLE      | tmp   | ref  | ix_ics        | ix_ics | 2       | const | 1500178 | Using where; Using index |
+----+-------------+-------+------+---------------+--------+---------+-------+---------+--------------------------+
1 row in set (0.00 sec)

查询结果:tudou@gyyx

mysql> SELECT a.* FROM tmp a WHERE id in(2700002,2700005,2700008,2700011,2700014,2700017,2700020,2700023,2700026,2700029,2700032,2700035,2700038,2700041,2700044,2700047,2700050,2700053,2700056,2700059);
+---------+---------------------+------+
| id      | ctime               | stat |
+---------+---------------------+------+
| 2700002 | 2012-04-19 15:52:13 | 0    |
| 2700005 | 2012-04-19 15:52:13 | 0    |
| 2700008 | 2012-04-19 15:52:13 | 0    |
| 2700011 | 2012-04-19 15:52:13 | 0    |
| 2700014 | 2012-04-19 15:52:13 | 0    |
| 2700017 | 2012-04-19 15:52:13 | 0    |
| 2700020 | 2012-04-19 15:52:13 | 0    |
| 2700023 | 2012-04-19 15:52:13 | 0    |
| 2700026 | 2012-04-19 15:52:13 | 0    |
| 2700029 | 2012-04-19 15:52:13 | 0    |
| 2700032 | 2012-04-19 15:52:13 | 0    |
| 2700035 | 2012-04-19 15:52:13 | 0    |
| 2700038 | 2012-04-19 15:52:13 | 0    |
| 2700041 | 2012-04-19 15:52:13 | 0    |
| 2700044 | 2012-04-19 15:52:13 | 0    |
| 2700047 | 2012-04-19 15:52:13 | 0    |
| 2700050 | 2012-04-19 15:52:13 | 0    |
| 2700053 | 2012-04-19 15:52:13 | 0    |
| 2700056 | 2012-04-19 15:52:13 | 0    |
| 2700059 | 2012-04-19 15:52:13 | 0    |
+---------+---------------------+------+
20 rows in set (0.00 sec)

优化查询:tudou@gyyx

mysql> SELECT a.* FROM tmp a
    -> INNER JOIN (SELECT id FROM tmp b WHERE b.stat=2 ORDER BY b.ctime DESC LIMIT 900000,20) c on c.id=a.id
    -> ;
+--------+---------------------+------+
| id     | ctime               | stat |
+--------+---------------------+------+
| 299999 | 2012-04-19 15:48:48 | 0    |
| 299996 | 2012-04-19 15:48:48 | 0    |
| 299993 | 2012-04-19 15:48:48 | 0    |
| 299990 | 2012-04-19 15:48:48 | 0    |
| 299987 | 2012-04-19 15:48:48 | 0    |
| 299984 | 2012-04-19 15:48:48 | 0    |
| 299981 | 2012-04-19 15:48:48 | 0    |
| 299978 | 2012-04-19 15:48:48 | 0    |
| 299975 | 2012-04-19 15:48:48 | 0    |
| 299972 | 2012-04-19 15:48:48 | 0    |
| 299969 | 2012-04-19 15:48:48 | 0    |
| 299966 | 2012-04-19 15:48:48 | 0    |
| 299963 | 2012-04-19 15:48:48 | 0    |
| 299960 | 2012-04-19 15:48:48 | 0    |
| 299957 | 2012-04-19 15:48:48 | 0    |
| 299954 | 2012-04-19 15:48:48 | 0    |
| 299951 | 2012-04-19 15:48:48 | 0    |
| 299948 | 2012-04-19 15:48:48 | 0    |
| 299945 | 2012-04-19 15:48:48 | 0    |
| 299942 | 2012-04-19 15:48:48 | 0    |
+--------+---------------------+------+
20 rows in set (0.60 sec)