mysql partition pruning not work

Question

I created a table with MySQL partition by hash(to_days(...)).

CREATE TABLE `requestlog` (
  `remotehost` varchar(40) DEFAULT NULL,
  `user` varchar(255) DEFAULT NULL,
  `request_time_str` varchar(40) DEFAULT NULL,
  `request_time` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
  `request_line` varchar(255) DEFAULT NULL,
  `status` int(11) DEFAULT NULL,
  `bytes` int(11) DEFAULT NULL,
  `referer` text,
  `useragent` text,
  `host` text,
  `instance` text,
  `ms` int(11) DEFAULT NULL,
  `cpu_ms` int(11) DEFAULT NULL,
  `api_cpu_ms` int(11) DEFAULT NULL,
  `cpm_usd` float DEFAULT NULL,
  `queue_name` varchar(40) DEFAULT NULL,
  `task_name` varchar(40) DEFAULT NULL,
  `loading_request` tinyint(1) DEFAULT NULL,
  `pending_ms` int(11) DEFAULT NULL,
  `exit_code` int(11) DEFAULT NULL,
  `throttle_code` int(11) DEFAULT NULL,
  `method` varchar(40) DEFAULT NULL,
  `path` varchar(255) DEFAULT NULL,
  `querystring` text,
  `protocol` varchar(40) DEFAULT NULL,
  `applog` text,
  `applog0` text,
  `applog1` text,
  `applog2` text,
  `applog3` text,
  `applog4` text,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `updated` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMES
TAMP,
  PRIMARY KEY (`request_time`,`id`),
  UNIQUE KEY `path` (`path`,`request_time`,`remotehost`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8
/*!50100 PARTITION BY HASH (to_days(request_time))
PARTITIONS 1000 */

However while I execute the following query. the explain partitions result shows the partition pruning not work because it scans all partitions belong to this table...

explain partitions select count(*) from requestlog where to_days(request_time) = '2012-08-01';

I tried the sample in this article. the explain partitions still shows it scan all partitions. how to partition a table by datetime column?

How to let the partition pruning works? Any hints?

Answer 1

try this without to_days:

explain partitions select count(*) from requestlog where request_time = '2012-08-01';

EDIT:

explain partitions 
        select count(*) 
        from requestlog 
        where request_time BETWEEN '2012-08-01 00:00:00' AND '2012-08-01 23:59:59';