Question

Ok, I have 2 million rows. Each has a billing date. i’m trying to partition this out by that date. I’ve made partitions. I’ve checked /var/lib/mysql and the files are there, all of an appropriate file size so I can see something’s working. However when I do explian paritions select, its still telling me it’s using all the partitions. Am I doing someething wrong with how I built the table? Query the table? Indexes?

CREATE TABLE `billing_bil` (
`id_bil` mediumint(9) unsigned NOT NULL AUTO_INCREMENT,
`bill_date_bil` date NOT NULL
PRIMARY KEY (`id`,`bill_date_bil`),
KEY `bill_date_bil` (`bill_date_bil`),
KEY `type_bill_date_bil` (`type_bil`,`bill_date_bil`)
) ENGINE=MyISAM AUTO_INCREMENT=2310168 DEFAULT CHARSET=latin1
/*!50100 PARTITION BY RANGE ( YEAR(bill_date_bil))
(PARTITION p0 VALUES LESS THAN (2008) ENGINE = MyISAM,
PARTITION p1 VALUES LESS THAN (2009) ENGINE = MyISAM,
PARTITION p2 VALUES LESS THAN (2010) ENGINE = MyISAM,
PARTITION p3 VALUES LESS THAN (2011) ENGINE = MyISAM,
PARTITION p4 VALUES LESS THAN (2012) ENGINE = MyISAM,
PARTITION p5 VALUES LESS THAN (2013) ENGINE = MyISAM,
PARTITION p6 VALUES LESS THAN (2014) ENGINE = MyISAM,
PARTITION p7 VALUES LESS THAN MAXVALUE ENGINE = MyISAM) */

EXPLAIN PARTITIONS SELECT SQL_NO_CACHE  id_bil FROM billing_bil WHERE bill_date_bil < '2010'
    id  select_type  table        partitions               type    possible_keys  key      key_len  ref        rows  Extra                   

---

 1  SIMPLE       billing_bil  p0,p1,p2,p3,p4,p5,p6,p7  index   bill_date_bil  PRIMARY  6        (NULL)  2310167  Using where; Using index

I was expecting that query to use p0 and p1 only, but it uses all of them.

Answer 1

Your partitions are fine. Your query’s WHERE clause is where the problem lies. When I ran the EXPLAIN PARTITIONS statement on MySQL 5.5, there were two warnings:

+---------+------+------------------------------------------------------------------+
| Level   | Code | Message                                                          |
+---------+------+------------------------------------------------------------------+
| Warning | 1292 | Incorrect date value: '2010' for column 'bill_date_bil' at row 1 |
| Warning | 1292 | Incorrect date value: '2010' for column 'bill_date_bil' at row 1 |
+---------+------+------------------------------------------------------------------+

If you change your query to use a real date like so, it will use the partitions (I didn’t include your indexes in my CREATE TABLE statement, which is why they aren’t being used):

mysql> EXPLAIN PARTITIONS SELECT SQL_NO_CACHE  id_bil FROM billing_bil WHERE bill_date_bil < '2010-01-01';
+----+-------------+-------------+------------+--------+---------------+------+---------+------+------+-------+
| id | select_type | table       | partitions | type   | possible_keys | key  | key_len | ref  | rows | Extra |
+----+-------------+-------------+------------+--------+---------------+------+---------+------+------+-------+
|  1 | SIMPLE      | billing_bil | p0,p1,p2   | system | NULL          | NULL | NULL    | NULL |    1 |       |
+----+-------------+-------------+------------+--------+---------------+------+---------+------+------+-------+

I’m guessing it uses partition p2 because MySQL supports partial dates (2010-00-00 is less than 2010-01-01): How to deal with "partial" dates (2010-00-00) from MySQL in Django?