MySQL 表分区梳理

本篇侧重mysql 表分区之 range partioning

分区表达式在指定范围内，分区应当是连续的，不重叠的，使用 VALUES LESS THAN 操作符定义。

employees 表用来记录有20个店的音箱连锁店。表：

CREATE TABLE employees (
id INT NOT NULL,
fname VARCHAR(30),
lname VARCHAR(30),
hired DATE NOT NULL DEFAULT '1970-01-01',
separated DATE NOT NULL DEFAULT '9999-12-31',
job_code INT NOT NULL,
store_id INT NOT NULL
);

<一> 比如按照 store_id 进行分区。

CREATE TABLE employees (
id INT NOT NULL,
fname VARCHAR(30),
lname VARCHAR(30),
hired DATE NOT NULL DEFAULT '1970-01-01',
separated DATE NOT NULL DEFAULT '9999-12-31',
job_code INT NOT NULL,
store_id INT NOT NULL
)
PARTITION BY RANGE (store_id) (
PARTITION p0 VALUES LESS THAN (6),
PARTITION p1 VALUES LESS THAN (11),
PARTITION p2 VALUES LESS THAN (16),
PARTITION p3 VALUES LESS THAN (21)
);

1到5号商店的雇员存储在 p0分区表中，6到10号商店雇员存储在p1分区表中......

但是问题来了，如果sotre_id 是21 ，将怎么存储呢？mysql 将会抛出错误。因为mysql 不知道store_id > 20的商店雇员存储在哪里。所以应该这么修改，

CREATE TABLE employees (
id INT NOT NULL,
fname VARCHAR(30),
lname VARCHAR(30),
hired DATE NOT NULL DEFAULT '1970-01-01',
separated DATE NOT NULL DEFAULT '9999-12-31',
job_code INT NOT NULL,
store_id INT NOT NULL
)
PARTITION BY RANGE (store_id) (
PARTITION p0 VALUES LESS THAN (6),
PARTITION p1 VALUES LESS THAN (11),
PARTITION p2 VALUES LESS THAN (16),    PARTITION p3 VALUES LESS THAN MAXVALUE);

MAXVALUE 所表示的整数值，比最大的整数值还要大(在数学意义上， 它是整数值的最小边界)。

说明：当数据量很大的时候，可以通过 alter table 的方式，将比如21到25的表数据置于p4 分区中。

<二>按job_code 分区

CREATE TABLE employees (
id INT NOT NULL,
fname VARCHAR(30),
lname VARCHAR(30),
hired DATE NOT NULL DEFAULT '1970-01-01',
separated DATE NOT NULL DEFAULT '9999-12-31',
job_code INT NOT NULL,
store_id INT NOT NULL
)
PARTITION BY RANGE (job_code) (
PARTITION p0 VALUES LESS THAN (100),
PARTITION p1 VALUES LESS THAN (1000),
PARTITION p2 VALUES LESS THAN (10000)
);

<三>按separated 分区

CREATE TABLE employees (
id INT NOT NULL,
fname VARCHAR(30),
lname VARCHAR(30),
hired DATE NOT NULL DEFAULT '1970-01-01',
separated DATE NOT NULL DEFAULT '9999-12-31',
job_code INT,
store_id INT
)
PARTITION BY RANGE ( YEAR(separated) ) (
PARTITION p0 VALUES LESS THAN (1991),
PARTITION p1 VALUES LESS THAN (1996),
PARTITION p2 VALUES LESS THAN (2001),
PARTITION p3 VALUES LESS THAN MAXVALUE
);

<四>按 timestamp 分区，利用 UNIX_TIMESTAMP() 函数

说明：mysql 5.5.1 后，timestamp 只允许使用UNIX_TIMESTAMP 函数。

CREATE TABLE quarterly_report_status (
report_id INT NOT NULL,
report_status VARCHAR(20) NOT NULL,
report_updated TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)
PARTITION BY RANGE ( UNIX_TIMESTAMP(report_updated) ) (
PARTITION p0 VALUES LESS THAN ( UNIX_TIMESTAMP('2008-01-01 00:00:00') ),
PARTITION p1 VALUES LESS THAN ( UNIX_TIMESTAMP('2008-04-01 00:00:00') ),
PARTITION p2 VALUES LESS THAN ( UNIX_TIMESTAMP('2008-07-01 00:00:00') ),
PARTITION p3 VALUES LESS THAN ( UNIX_TIMESTAMP('2008-10-01 00:00:00') ),
PARTITION p4 VALUES LESS THAN ( UNIX_TIMESTAMP('2009-01-01 00:00:00') ),
PARTITION p5 VALUES LESS THAN ( UNIX_TIMESTAMP('2009-04-01 00:00:00') ),
PARTITION p6 VALUES LESS THAN ( UNIX_TIMESTAMP('2009-07-01 00:00:00') ),
PARTITION p7 VALUES LESS THAN ( UNIX_TIMESTAMP('2009-10-01 00:00:00') ),
PARTITION p8 VALUES LESS THAN ( UNIX_TIMESTAMP('2010-01-01 00:00:00') ),
PARTITION p9 VALUES LESS THAN (MAXVALUE)
);

<五>.删除旧分区

比如删除 employees 分区p0

ALTER TABLE employees DROP PARTITION p0

另一种方式，如：

DELETE FROM employees WHERE YEAR(separated) <= 1990

但是，按分区删除的效率是比较高的。

<六>.在分区上查找数据

EXPLAIN PARTITIONS SELECT COUNT(*) FROM employees
WHERE separated BETWEEN '2000-01-01' AND '2000-12-31' GROUP BY store_id;,

mysql 知道分区p2 需要被扫描，而其它分区则不包含符合条件的记录。

<七>.按Range Columns 进行分区

使用DATE 或者 DATETIME 列作为分区列，通过 RANGE COLUMNN 进行分区。

CREATE TABLE members (
firstname VARCHAR(25) NOT NULL,
lastname VARCHAR(25) NOT NULL,
username VARCHAR(16) NOT NULL,
email VARCHAR(35),
joined DATE NOT NULL
)
PARTITION BY RANGE COLUMNS(joined) (
PARTITION p0 VALUES LESS THAN ('1960-01-01'),
PARTITION p1 VALUES LESS THAN ('1970-01-01'),
PARTITION p2 VALUES LESS THAN ('1980-01-01'),
PARTITION p3 VALUES LESS THAN ('1990-01-01'),
PARTITION p4 VALUES LESS THAN MAXVALUE
);