Mysql 数据库表分区

前言：当数据库存储数据达到一定量级时，传统的数据读取会扫描许多不需要的数据，而真正所用的数据却可能只有几行。因此，对于几百g以上的数据库，有必要采取数据库分区，以分区的形式来划分数据库存储，这种方式对用户的操作来说是透明的，只需要将读取数据时加上分区形式的字段就可以达到分区的效果，提升读写速度，降低对数据库的资源使用。但是对于数据库使用人员来说，必须要加上相关的分区字段，而且不能跨区，否则就不会有分区的效果。

分区的方式也有很多种，今天介绍我们采用较多的一种分区方式，按date进行划分。分区时可以以月划分，以周划分，以天划分，都可以。主要取决于数据的集中情况。

相关的表分区语句介绍如下：

1.先创建一个新的表，并且分区。再将数据从原表导入。

数据库表分区相关语句功能

查看表分区数据，查看全量数据量

USE information_schema;

SELECT PARTITION_NAME,TABLE_ROWS
FROM INFORMATION_SCHEMA.PARTITIONS
WHERE TABLE_NAME = 'talbles_name';

SELECT table_name,table_rows FROM TABLES 
WHERE TABLE_SCHEMA = 'db_name' 
ORDER BY table_rows DESC

;

#判断当前MySQL是否支持分区？
show variables like '%partition%';
#查看表分区情况
select partition_name part,partition_expression expr,partition_description descr,table_rows from information_schema.partitions  where table_schema = schema()  and table_name='test'; 

#创建新表，并且表分区，以月为单位
CREATE TABLE `apdailysts_p` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `ap_id` INT(11) NOT NULL,
  `mac` VARCHAR(17) NOT NULL,
  `liveinfo` LONGTEXT NOT NULL,
  `livetime` INT(11) NOT NULL,
  `stsdate` DATE NOT NULL,
  `lastmodified` DATETIME NOT NULL,
   PRIMARY KEY (`id`, `stsdate`)
) 
PARTITION BY RANGE COLUMNS(stsdate) (
    PARTITION p0 VALUES LESS THAN ('2016-06-01'),
    PARTITION p1 VALUES LESS THAN ('2016-07-01'),
    PARTITION p2 VALUES LESS THAN ('2016-08-01'),
    PARTITION p3 VALUES LESS THAN ('2016-09-01'),
    PARTITION p15 VALUES LESS THAN MAXVALUE
)

2.直接修改表结构，达到分区的效果，这种会创建临时表，比较耗费资源（会覆盖以前的分区），第一次分区的话，需要将字段修改为date 类型，并添加至主键

ALTER TABLE question_P PARTITION BY RANGE (Month(send_time))
(   
PARTITION p_Apr VALUES LESS THAN (TO_DAYS('2017-10-01')),
PARTITION p_May VALUES LESS THAN (TO_DAYS('2017-11-01')), 
PARTITION p_Dec VALUES LESS THAN MAXVALUE )

3.修改datetime字段的表分区

3.1创建新表并分区

CREATE TABLE `t_ask_unit_re` (
  `id` varchar(32) NOT NULL COMMENT '主键',
  `create_time` datetime NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT '创建时间',
  `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`,`create_time`)
) partition by range(to_days(create_time)) (
    partition p201708 values less than (to_days('2017-09-01')),
    partition p201709 values less than (to_days('2017-10-01')),
    partition p201710 values less than (to_days('2017-11-01')),    
    partition p201711 values less than (to_days('2017-12-01')),
    partition p201712 values less than (to_days('2018-01-01')),   
    PARTITION p202XYZ VALUES LESS THAN (MAXVALUE));

3.2alter 方式直接修改表分区

alter table t_ask_123 partition by range(to_days(create_time)) (
    partition p201708 values less than (to_days('2017-09-01')),
    partition p201709 values less than (to_days('2017-10-01')),
    partition p201710 values less than (to_days('2017-11-01')),    
    partition p201711 values less than (to_days('2017-12-01')),
    partition p201712 values less than (to_days('2018-01-01')),    
    partition p201801 values less than (to_days('2018-02-01')),     
    partition p201802 values less than (to_days('2018-03-01')),
    partition p201803 values less than (to_days('2018-04-01')),
    partition p201804 values less than (to_days('2018-05-01')),  
    partition p201805 values less than (to_days('2018-06-01')),
    partition p201806 values less than (to_days('2018-07-01')),  
    partition p201807 values less than (to_days('2018-08-01')),  
    partition p201808 values less than (to_days('2018-09-01')),  
    partition p201809 values less than (to_days('2018-10-01')),  
    partition p201810 values less than (to_days('2018-11-01')),  
    partition p201811 values less than (to_days('2018-12-01')),    
    partition p201812 values less than (to_days('2019-01-01')),  
    partition p201901 values less than (to_days('2019-02-01')),   
    partition p201902 values less than (to_days('2019-03-01')),
    partition p201903 values less than (to_days('2019-04-01')),  
    partition p201904 values less than (to_days('2019-05-01')),
    partition p201905 values less than (to_days('2019-06-01')),  
    partition p201906 values less than (to_days('2019-07-01')),
    partition p201907 values less than (to_days('2019-08-01')),  
    partition p201908 values less than (to_days('2019-09-01')),  
    partition p201909 values less than (to_days('2019-10-01')),
    partition p201910 values less than (to_days('2019-11-01')),    
    partition p201911 values less than (to_days('2019-12-01')),  
    partition p201912 values less than (to_days('2020-01-01')),   
    partition p202001 values less than (to_days('2020-02-01')),
    partition p202002 values less than (to_days('2020-03-01')),
    partition p202003 values less than (to_days('2020-04-01')),
    partition p202004 values less than (to_days('2020-05-01')),
    partition p202005 values less than (to_days('2020-06-01')),
    partition p202006 values less than (to_days('2020-07-01')),
    partition p202007 values less than (to_days('2020-08-01')),
    partition p202008 values less than (to_days('2020-09-01')),
    partition p202009 values less than (to_days('2020-10-01')),
    partition p202010 values less than (to_days('2020-11-01')),
    partition p202011 values less than (to_days('2020-12-01')),
    partition p202012 values less than (to_days('2021-01-01')),
    PARTITION p202XYZ VALUES LESS THAN (MAXVALUE));