MySQL Partition by Range on YEAR(date) wrong results - mysql

Question

I have a table defined as below:
CREATE TABLE `adverts_stats_clicks` (
`advert_stats_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`advertisment_id` int(10) unsigned NOT NULL DEFAULT '0',
`domain_id` int(10) unsigned NOT NULL DEFAULT '0',
`catdom_id` int(10) unsigned NOT NULL DEFAULT '0',
`added_on` date NOT NULL DEFAULT '0000-00-00',
`ipfrom` varchar(64) NOT NULL DEFAULT '',
`click_on` varchar(10) NOT NULL DEFAULT '',
`click_from` varchar(5) NOT NULL DEFAULT '',
`click_from_path` char(3) NOT NULL DEFAULT '',
`country_id` int(11) NOT NULL DEFAULT '0',
PRIMARY KEY (`advert_stats_id`,`added_on`),
KEY `domain_id` (`domain_id`),
KEY `click_on` (`click_on`),
KEY `advertisment_id` (`advertisment_id`),
KEY `country_id` (`country_id`),
KEY `added_on` (`added_on`)
) ENGINE=MyISAM AUTO_INCREMENT=48176808 DEFAULT CHARSET=latin1
/*!50100 PARTITION BY RANGE (YEAR(added_on))
(PARTITION ac0 VALUES LESS THAN (2005) ENGINE = MyISAM,
PARTITION ac1 VALUES LESS THAN (2006) ENGINE = MyISAM,
PARTITION ac2 VALUES LESS THAN (2007) ENGINE = MyISAM,
PARTITION ac3 VALUES LESS THAN (2009) ENGINE = MyISAM,
PARTITION ac4 VALUES LESS THAN (2010) ENGINE = MyISAM,
PARTITION ac5 VALUES LESS THAN (2011) ENGINE = MyISAM,
PARTITION ac6 VALUES LESS THAN (2012) ENGINE = MyISAM,
PARTITION ac7 VALUES LESS THAN (2013) ENGINE = MyISAM,
PARTITION ac8 VALUES LESS THAN (2014) ENGINE = MyISAM,
PARTITION ac9 VALUES LESS THAN (2015) ENGINE = MyISAM,
PARTITION ac99 VALUES LESS THAN MAXVALUE ENGINE = MyISAM) */
Then if I run the following query:
SELECT advert_stats_id
FROM adverts_stats_clicks
WHERE domain_id = 618
AND click_on = 'www'
AND click_from IN('sel','top','s','e','adv')
AND advertisment_id = 6122
AND added_on BETWEEN '2012-10-01' AND '2014-12-31';
I get for example 152 results. But if I change the date range as fllows:
SELECT advert_stats_id
FROM adverts_stats_clicks
WHERE domain_id = 618
AND click_on = 'www'
AND click_from IN('sel','top','s','e','adv')
AND advertisment_id = 6122
AND added_on BETWEEN '2013-10-01' AND '2014-12-31';
I get 643 results. Which is nonsense as the previous date range is bigger than the second.
If I run explain partitions I get the following:
id select_type table partitions type possible_keys key key_len ref rows Extra
1 SIMPLE adverts_stats_clicks ac7,ac8,ac9 index_merge domain_id,click_on,advertisment_id,added_on advertisment_id,domain_id 4,4 NULL 114 Using intersect(advertisment_id,domain_id); Using where
So in the first query the correct partitions (ac7,ac8,ac9) were selected. This proves that pruning is working. For the second query also the correct partitions were selected (ac8, ac9) however the results retrieved by both cannot be trusted.
What is happening ??? Why is like this?
Some extra info from sever variables in case it might me important to figure out.
Variable_name Value
character_set_client utf8mb4
character_set_connection utf8mb4
character_set_database latin1
character_set_filesystem binary
character_set_results utf8mb4
character_set_server latin1
character_set_system utf8
character_sets_dir /usr/share/mysql/charsets/
Please help and ask additional questions if you need more info in order to help.
Thank you!

Answer 1

when you are using BETWEEN '2013-10-01' AND '2014-12-31';
your checking a value in between two strings...
'2013-10-01' will take as a string...
so if we want to check between the dates..string should be converted to dates..
use str_to_date() function