关于Oracle 10g 中通过DBLink访问MySQL数据库

1, 首先在Oracle所在计算机安装MySQL的Client端软件，并且x86_64和i386版本的都需要安装，以便可以连接MySQL数据库。查看Client安装情况：
rpm -qa |grep mysql
mysql-5.0.45-7.el5
mysql-5.0.45-7.el5
得到两条记录，一条是x86_64的，一条是i386的。
如果看到还没有安装mysql客户端软件，则需要安装:
yum install mysql
yum install mysql.i386
验证在此Oracle所在计算机是可以连接目标主机MySQL数据库:
mysql -h 192.168.1.1 -u root -p mysql

2, 检查Oracle所在计算机是否已安装MySQL ODBC客户端，并且x86_64和i386版本的都需要安装。
rpm -qa |grep mysql-connect
如果没有安装mysql-connector-odbc，则用下面命令下载和安装：
下载 mysql-connector-odbc：
wget ftp://mirror.switch.ch/pool/3/mirror/centos/5.2/os/i386/CentO S/mysql-connector-odbc-3.51.12-2.2.i386.rpm
安装mysql-connector-odbc：
rpm -ivh mysql-connector-odbc-3.51.12-2.2.i386.rpm
得到提示 libltdl.so.3 is needed by mysql-connector-odbc-3.51.12-2.2.i386 ，发现需要安装libtool的i386版本，因此通过如下命令安装libtool-ltdl.i386：
yum list *.i386|grep libtool
yum install libtool-ltdl.i386

3, 在Oracle所在计算机编辑/etc/odbc.ini文件,测试ODBC工作
vi /etc/odbc.ini
#odbc.ini内容如下
[test]
Driver=/usr/lib64/libmyodbc3.so
Description=MySQL
Server=192.168.1.1(MySQL Server IP)
Port=3306
User= (MySQL Username)
UID= (MySQL Username）
Password= (MySQL PWD)
Database= (MySQL Database Name)
Option=3
Socket=
在命令行中执行下列命令，应能够顺利登入MySQL Client窗口，即证明ODBC功能正常：
isql -v test
quit

4, 编辑hs配置文件 vi /ora10g/hs/admin/inittest.ora(注意文件名中蓝色部分为odbc.ini中蓝色名称)
HS_FDS_CONNECT_INFO = test
HS_FDS_TRACE_LEVEL = on（正式使用后，不需要排错的时候应设为off）
HS_FDS_TRACE_FILE_NAME = test.trc
HS_FDS_SHAREABLE_NAME=/usr/lib/libmyodbc3.so
set ODBCINI=/etc/odbc.ini

5, 编辑Oracle所在计算机的Oracle listener的配置文件，建立一个模拟Oracle Listener的监听方式,为将来建立dblink做准备：
vi /ora10g/network/admin/listener.ora 加入如下语句：
(SID_DESC =
(SID_NAME = test)
(ORACLE_HOME = /ora10g)
(PROGRAM = hsodbc)
(ENVS=LD_LIBRARY_PATH=/ora10g/lib32:/usr/lib64:/ora10g/lib)
)
listener.ora文件现在的内容变成：
SID_LIST_LISTENER = (
SID_LIST =
(SID_DESC =
(ORACLE_HOME = /ora10g)
(PROGRAM = extproc)
(GLOBAL_DBNAME=prod)
(SID_NAME=prod)
)
(SID_DESC =
(SID_NAME = test)
(ORACLE_HOME = /ora10g)
(PROGRAM = hsodbc)
(ENVS=LD_LIBRARY_PATH=/ora10g/lib32:/usr/lib64:/ora10g/lib)
)
)
LISTENER = (
DESCRIPTION_LIST =
(DESCRIPTION = (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
(ADDRESS = (PROTOCOL = TCP)(HOST = 0.0.0.0)(PORT = 1521)) )
)
执行lsnrctl reload使Listener生效：
su – oracle
lsnrctl reload
LSNRCTL for Linux: Version 10.2.0.4.0 – Production on 09-FEB-2009 13:59:38 Copyright (c) 1991, 2007, Oracle.
All rights reserved. Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1)))
The command completed successfully
lsnrctl status
LSNRCTL for Linux: Version 10.2.0.4.0 – Production on 12-FEB-2009 08:56:00

Copyright (c) 1991, 2007, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1)))
STATUS of the LISTENER
————————
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 10.2.0.4.0 – Production
Start Date                03-JAN-2009 03:47:39
Uptime                    40 days 5 hr. 8 min. 20 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /ora10g/network/admin/listener.ora
Listener Log File         /ora10g/network/log/listener.log
Listening Endpoints Summary…
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=0.0.0.0)(PORT=1521)))
Services Summary…
Service “PLSExtProc” has 1 instance(s).
Instance “PLSExtProc”, status UNKNOWN, has 1 handler(s) for this service…
Service “test” has 1 instance(s).
Instance “test”, status UNKNOWN, has 1 handler(s) for this service…
The command completed successfully

6, 编辑Oracle所在计算机中的tnsnames.ora文件，便于建立dblink。注意，此tnsnames的配置可以支持tnsping,但是不能支持sqlplus登录，只用于dblink：
vi /ora10g/network/admin/tnsnames.ora
test =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
(CONNECT_DATA =
(SID = test)
)
(HS = OK)
)

7, 在Oracle Database建立dblink:
create public database link MYSQL
connect to “mysql username” identified by “mysql pwd”
using ‘(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP) (HOST = 127.0.0.1) (PORT =1521) )
(CONNECT_DATA = (SID= test) )
(HS=OK)
)’;
要注意用户名和密码处需要用双引号，否则Oracle所传输的都是大写字母，可能无法登录进入MySQL。

8, 由于MySQL中的表名的大小写敏感，因此需要在进行SQL查询时对表名用双引号扩起来
select * from “tablename”@test