在实际工作中，我们可能会遇到需要操作其他数据库实例的部分表，但又不想系统连接多库。此时我们就需要用到数据表映射。如同Oracle中的DBlink一般，使用过Oracle DBlink数据库链接的人都知道可以跨实例来进行数据查询，同样的，MySQL自带的FEDERATED引擎完美的帮我们解决了该问题。本篇文章介绍FEDERATED引擎的开启和使用。
1.开启FEDERATED引擎
若需要创建FEDERATED引擎表，则目标端实例要开启FEDERATED引擎。从MySQL5.5开始FEDERATED引擎默认安装 只是没有启用，进入命令行输入 show engines ; FEDERATED行状态为NO。
mysql> show engines; +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | | MyISAM | YES | MyISAM storage engine | NO | NO | NO | | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | ARCHIVE | YES | Archive storage engine | NO | NO | NO | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | | FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 9 rows in set (0.00 sec)
2.使用CONNECTION创建FEDERATED表
使用CONNECTION创建FEDERATED引擎表通用模型：
CREATE TABLE (......) ENGINE =FEDERATED CONNECTION='mysql://username:password@hostname:port/database/tablename'
简单创建测试：
# 源端表结构及数据 mysql> show create table test_table\G *************************** 1. row *************************** Table: test_table Create Table: CREATE TABLE `test_table` ( `increment_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增主键', `stu_id` int(11) NOT NULL COMMENT '学号', `stu_name` varchar(20) DEFAULT NULL COMMENT '学生姓名', `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间', `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间', PRIMARY KEY (`increment_id`), UNIQUE KEY `uk_stu_id` (`stu_id`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 COMMENT='学生表' 1 row in set (0.00 sec) mysql> select * from test_table; +--------------+--------+----------+---------------------+---------------------+ | increment_id | stu_id | stu_name | create_time | update_time | +--------------+--------+----------+---------------------+---------------------+ | 1 | 1001 | wang | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 2 | 1002 | dfsfd | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 3 | 1003 | fdgfg | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 4 | 1004 | sdfsdf | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 5 | 1005 | dsfsdg | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 6 | 1006 | fgd | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | +--------------+--------+----------+---------------------+---------------------+ 6 rows in set (0.00 sec) # 目标端建表及查询 # 注意ENGINE=FEDERATED CONNECTION后为源端地址 避免使用带@的密码 mysql> CREATE TABLE `test_table` ( -> `increment_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '自增主键', -> `stu_id` int(11) NOT NULL COMMENT '学号', -> `stu_name` varchar(20) DEFAULT NULL COMMENT '学生姓名', -> `create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间', -> `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改时间', -> PRIMARY KEY (`increment_id`), -> UNIQUE KEY `uk_stu_id` (`stu_id`) -> ) ENGINE=FEDERATED DEFAULT CHARSET=utf8 COMMENT='学生表' CONNECTION='mysql://root:root@10.50.60.212:3306/source/test_table'; Query OK, 0 rows affected (0.01 sec) mysql> select * from test_table; +--------------+--------+----------+---------------------+---------------------+ | increment_id | stu_id | stu_name | create_time | update_time | +--------------+--------+----------+---------------------+---------------------+ | 1 | 1001 | wang | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 2 | 1002 | dfsfd | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 3 | 1003 | fdgfg | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 4 | 1004 | sdfsdf | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 5 | 1005 | dsfsdg | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | | 6 | 1006 | fgd | 2019-06-21 10:52:03 | 2019-06-21 10:52:03 | +--------------+--------+----------+---------------------+---------------------+ 6 rows in set (0.00 sec)
3.使用CREATE SERVER创建FEDERATED表