MySQL中dblink的实现

参照以下博客：http://blog.csdn.net/renfengjun/article/details/18730977

最近项目中涉及MySQL数据库视图的创建，需要整合两个位于不同服务器上数据库的内容，就遇到了远程访问数据库的问题。在cracle中可以通过dblink来实现跨本地数据库来访问另外一个数据库中的数据。通过在网上查找，发现可以通过MySQL中的federated插件来实现类似的功能。

操作环境：

宿主机为win8系统，MySQL数据库，ip：192.168.1.98；从机为VMware虚拟机中的Linux系统，版本为CentOS6.5，MySQL数据库，ip：192.168.1.106。

实现功能：

可以在Linux系统中MySQL数据库（target端）中建立宿主机MySQL数据库（source端）中某个表的link，当在Linux中读取link表时，就相当于直接读取宿主机中的原始表内容。

实现步骤：

1. 查看target端（Linux虚拟机中）是否安装了federated插件：

mysql> show engines;

+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints
|
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO        
|
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO        
|
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO        
|
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | 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      
|
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO        
|
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES       
|
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO        
|
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

显示没有安装federated插件

2. 安装federated插件：

mysql>install
plugin federated soname 'ha_federated.so';

ERROR
1125 (HY000): Function 'federated' already exists

说明已经安装过了，但没有启用

[root@localhost
etc]# service mysql stop

[root@localhost
etc]# mysqld_safe --federated &

[root@localhost
etc]# 140811 01:20:
1161f
21 mysqld_safe Logging to '/var/lib/mysql/localhost.localdomain.err'.

140811 01:20:22 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

mysql>
show engines;

+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| FEDERATED          |YES     
| Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

federated插件已经启用

3.
配置/etc/my.conf，设置federated为默认启动

[root@localhost
etc]# vi /etc/my.conf

在文件中加入一行：

federated

重启mysql服务

service
mysql restart

mysql>
show engines;

+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| FEDERATED          | YES      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

已经设置为默认启动了。

4.
在source端建立测试表，我是通过Navicat建立表的，其sql文件为：

DROP
TABLE IF EXISTS `e_eledata`;

CREATE TABLE `e_eledata` (

  `ID` bigint(20) unsigned NOT NULL auto_increment COMMENT 'ID',

  `E_ELEMETERHEAD_ID` bigint(20) default NULL COMMENT '电表表头ID',

 `DAQDT` timestamp NULL default NULL COMMENT '数据采集时间',

  `DLDT` timestamp NULL default NULL COMMENT '数据入库时间',

  `APCURRENT` decimal(10,3) default NULL COMMENT 'A相电流。单位：A。',

 `BPCURRENT` decimal(10,3) default NULL COMMENT 'B相电流。单位：A。',

  `CPCURRENT` decimal(10,3) default NULL COMMENT 'C相电流。单位：A。',

 `APVOLTAGE` decimal(10,3) default NULL COMMENT 'A相电压。单位：V。',

  `BPVOLTAGE` decimal(10,3) default NULL COMMENT 'B相电压。单位：V。',

  `CPVOLTAGE` decimal(10,3) default NULL COMMENT 'C相电压。单位：V。',

  PRIMARY KEY  (`ID`)

) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 COMMENT='电路数据表';

5.
在target端建立link表，可以直接改写source表的sql脚本文件为：

DROP
TABLE IF EXISTS `e_eledata_link`;

CREATE TABLE `e_eledata_link`
(

  `ID` bigint(20) unsigned NOT NULL auto_increment COMMENT 'ID',

  `E_ELEMETERHEAD_ID` bigint(20) default NULL COMMENT '电表表头ID',

 `DAQDT` timestamp NULL default NULL COMMENT '数据采集时间',

  `DLDT` timestamp NULL default NULL COMMENT '数据入库时间',

  `APCURRENT` decimal(10,3) default NULL COMMENT 'A相电流。单位：A。',

 `BPCURRENT` decimal(10,3) default NULL COMMENT 'B相电流。单位：A。',

  `CPCURRENT` decimal(10,3) default NULL COMMENT 'C相电流。单位：A。',

 `APVOLTAGE` decimal(10,3) default NULL COMMENT 'A相电压。单位：V。',

  `BPVOLTAGE` decimal(10,3) default NULL COMMENT 'B相电压。单位：V。',

  `CPVOLTAGE` decimal(10,3) default NULL COMMENT 'C相电压。单位：V。',

  PRIMARY KEY  (`ID`)

) ENGINE=FEDERATEDAUTO_INCREMENT=1DEFAULT
CHARSET=utf8 COMMENT='电路数据表'

CONNECTION='mysql://usrname:password@192.168.1.98:3306/databasename/table

其中：

usrname为宿主机中MySQL的用户名

password为相应的密码

（要保证该用户具有远程登陆的权限，可以通过以下命令来设置：

mysql>GRANT ALL PRIVILEGES ON *.* TO 'usrname'@'%' IDENTIFIED BY 'password' WITH GRANT OPTION;

其中*.*是指对用户开放所有数据库和表的权限，如果只开放某一个数据库的一个表为databasename.table；'%'指的是该用户可以从任意的一个ip地址来远程访问数据库，包括本地，如果要限制用户从特定的ip来访问，将其改为'ip地址'）

192.168.1.98是source数据库的ip，这里为我宿主机的ip

3306为数据库的端口，默认一般为3306

database 和table分别为source端数据库的名称和表名称

将该sql脚本在target端运行

6. 实现跨本地数据库的访问

在target端通过访问e_eledata_link表来访问source端e_eledata表

mysql>
select *from e_eledata_link;