mysql - 分区表使用所有分区用于 MySQL 中的基本 SELECT 语句

Question

我在 MySQL 中有一个表，该表按 year(date) 的函数进行 HASH 分区。目标是每年或多或少将我的数据分配到一个分区中。

当执行一个基本的 select 语句时:

EXPLAIN PARTITIONS
SELECT date 
FROM date_table 
WHERE date >= '2008-01-01' AND date <= '2009-01-01'

...正在使用所有分区。我假设最多只使用部分分区，最多 2 个。关于分区的工作方式，我在这里遗漏了什么？

测试.sql

DROP TABLE IF EXISTS `tmp_date_table`;

CREATE TABLE `tmp_date_table` (
    `date_id` INT(11) NOT NULL,
    `date` DATE NOT NULL,
    PRIMARY KEY (`date_id`, `date`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
PARTITION BY HASH (year(date))
PARTITIONS 11 
;

INSERT INTO `tmp_date_table`(date_id, date) 
VALUES
(1, '2000-01-01'),
(2, '2001-01-01'),
(3, '2002-01-01'),
(4, '2003-01-01'),
(5, '2004-01-01'),
(6, '2005-01-01'),
(7, '2006-01-01'),
(8, '2007-01-01'),
(9, '2008-01-01'),
(10, '2009-01-01'),
(11, '2010-01-01');

EXPLAIN PARTITIONS
SELECT date FROM tmp_date_table WHERE date >= '2008-01-01' AND date <= '2009-01-01';

DROP TABLE IF EXISTS `tmp_date_table`;

感谢任何帮助。

Answer 1

所以看起来你设置正确，我挖得更深一些。

http://dev.mysql.com/doc/refman/5.7/en/partitioning-pruning.html

When a table is partitioned by HASH or [LINEAR] KEY, pruning can be used only on integer columns. For example, this statement cannot use pruning because dob is a DATE column:

SELECT * FROM t4 WHERE dob >= '2001-04-14' AND dob <= '2005-10-15';

所以你不能用 HASH 做你正在做的事情。

However, if the table stores year values in an INT column, then a query having WHERE year_col >= 2001 AND year_col <= 2005 can be pruned.

这对我来说似乎违反直觉，但部分交易是您必须始终指定分区的数量预先(在您的情况下为 11)，因此分区是计算出来的因此:

If you insert a record into t1 whose col3 value is '2005-09-15', then the partition in which it is stored is determined as follows:

MOD(YEAR('2010-09-01'),11)
=  MOD(2010,11)
=  8

所以这将进入分区 8 而不是分区 11，这意味着:

MOD(YEAR('2000-09-01'),11)
=  MOD(2000,11)
=  9

您的第一年将进入分区 9。如果您仅查询日期，它将使用正确的分区:

WHERE date = "2010-01-01"

但不在范围内。

由于您的数据范围是已知的，而且看起来都是历史数据，因此您将不得不硬着头皮为每年设置一个范围。但是，通过这种方式，当您使用 BETWEEN 时，您的范围查询将仅使用正确的分区。

DROP TABLE IF EXISTS `tmp_date_table`;

CREATE TABLE `tmp_date_table` (
    `date_id` INT(11) NOT NULL,
    `dates` DATE NOT NULL
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
PARTITION BY RANGE ( YEAR(`dates`) ) (
    PARTITION p0 VALUES LESS THAN (2001),
    PARTITION p1 VALUES LESS THAN (2002),
    PARTITION p2 VALUES LESS THAN (2003),
    PARTITION p3 VALUES LESS THAN (2004),
    PARTITION p4 VALUES LESS THAN (2005),
    PARTITION p5 VALUES LESS THAN (2006),
    PARTITION p6 VALUES LESS THAN (2007),
    PARTITION p7 VALUES LESS THAN (2009),
    PARTITION p8 VALUES LESS THAN (2010),
    PARTITION p9 VALUES LESS THAN (2011),
    PARTITION p10 VALUES LESS THAN MAXVALUE

);

INSERT INTO `tmp_date_table`(date_id, `dates`) 
VALUES
(1, '2000-01-01'),
(2, '2001-01-01'),
(3, '2002-01-01'),
(4, '2003-01-01'),
(5, '2004-01-01'),
(6, '2005-01-01'),
(7, '2006-01-01'),
(8, '2007-01-01'),
(9, '2008-01-01'),
(10, '2009-01-01'),
(11, '2010-01-01'),
(12, '2012-01-01');



EXPLAIN PARTITIONS
SELECT dates FROM tmp_date_table WHERE (`dates`) BETWEEN  "2001-01-01" and "2004-01-01" ;

DROP TABLE IF EXISTS `tmp_date_table`;