Oracle10g通过DBLink访问MySQL示例
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