PostgreSQL通过mysql_fdw访问MySQL数据库

Mysql与PostgreSQL的安装过程省略。

为简便起见，把MySQL和PostgreSQL都安装在一个机器上，然后在此机器上（准确地说是在PostgreSQL运行的机器上）安装mysql_fdw：

首先是下载 mysql_fdw：

http://pgxn.org/dist/mysql_fdw/

mysql_fdw-1.0.1.zip

然后是解压和安装：

[root@server mysql_fdw-1.0.1]# pwd
/soft/fdw/mysql_fdw-1.0.1
[root@server mysql_fdw-1.0.1]# ls
META.json  Makefile  README  mysql_fdw--1.0.sql  mysql_fdw.c  mysql_fdw.control 

运行 make 和 make install，其README文件说得很清楚：

[root@server mysql_fdw-1.0.1]# cat README
MySQL FDW for PostgreSQL 9.1+
==============================

This PostgreSQL extension implements a Foreign Data Wrapper (FDW) for
the MySQL.

This code is experimental, and largely intended as a pet project for me
to experiment with and learn about FDWs in PostgreSQL.

By all means use it, but do so entirely at your own risk! You have been
warned!

Building
--------

Install MySQL, or just the C client library, and Once that's done, the 
extension can be built with:

PATH=/usr/local/pgsql/bin/:/usr/local/mysql/bin:$PATH make USE_PGXS=1 
sudo PATH=/usr/local/pgsql/bin/:/usr/local/mysql/bin:$PATH make USE_PGXS=1 install

(assuming you have PostgreSQL 9.1 in /usr/local/pgsql and MySQL in 
/usr/local/mysql).

I've tested on Mac OS X 10.7 only, but other *nix's should also work.
I haven't tested on Windows, but the code should be good on MinGW.

Limitations
-----------

- No attempt is made to pushdown quals to MySQL.

- The MySQL connection used to plan queries isn't currently reused
  during execution.

Usage
-----

The following parameters can be set on a MySQL foreign server:

address:        The address or hostname of the MySQL server.
                Default: 127.0.0.1

port:           The port number on which the MySQL server is listening.
                Default: 3306

The following parameter can be set on a MySQL foreign table:

database:       The name of the MySQL database to query.
                Default: NULL

query:          An SQL query to define the data set on the MySQL server.

table:          The name of a table (quoted and qualified as required)
                on the MySQL table.

Note that the query and table paramters are mutually exclusive. Using
query can provide either a simple way to push down quals (which of
course is fixed at definition time), or to base remote tables on 
more complex SQL queries.

The following parameter can be set on a user mapping for a MySQL
foreign server:

username:       The username to use when connecting to MySQL
                Default <none>

password:       The password to authenticate to the MySQL server with.
                Default: <none>

Example
-------

-- Install the extension
CREATE EXTENSION mysql_fdw;

-- Create the foreign server, a pointer to the MySQL server.
CREATE SERVER mysql_svr 
    FOREIGN DATA WRAPPER mysql_fdw 
    OPTIONS (address '127.0.0.1', port '3306');

-- Create one or more foreign tables on the MySQL server. The first of 
-- these maps to a remote table, whilst the second uses an SQL query.
CREATE FOREIGN TABLE employees (
    id integer,
    name text,
    address text)
    SERVER mysql_svr
    OPTIONS (table 'hr.employees');

CREATE FOREIGN TABLE overtime_2010 (
    id integer,
    employee_id integer,
    hours integer)
    SERVER mysql_svr
    OPTIONS (query 'SELECT id, employee_id, hours FROM hr.overtime WHERE year = 2010;');

-- Create a user mapping to tell the FDW the username/password to 
-- use to connect to MySQL, for PUBLIC. This could be done on a per-
-- role basis.
CREATE USER MAPPING FOR PUBLIC 
    SERVER mysql_svr 
    OPTIONS (username 'dpage', password '');

-- 
Dave Page
dpage@pgadmin.org
[root@server mysql_fdw-1.0.1]#

[root@server mysql_fdw-1.0.1]# PATH=/usr/local/pgsql/bin/:/usr/local/mysql/bin:$PATH make USE_PGXS=1
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I/usr/local/mysql/include -I. -I. -I/usr/local/pgsql/include/server -I/usr/local/pgsql/include/internal -D_GNU_SOURCE   -c -o mysql_fdw.o mysql_fdw.c
mysql_fdw.c: In function 'mysqlPlanForeignScan':
mysql_fdw.c:395: 警告: 'rows' may be used uninitialized in this function
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wformat-security -fno-strict-aliasing -fwrapv -fpic -shared -o mysql_fdw.so mysql_fdw.o -L/usr/local/pgsql/lib  -Wl,-rpath,'/usr/local/pgsql/lib',--enable-new-dtags  -L/usr/local/mysql/lib -lmysqlclient -lpthread -lm -lrt -ldl 
[root@server mysql_fdw-1.0.1]# sudo PATH=/usr/local/pgsql/bin/:/usr/local/mysql/bin:$PATH make USE_PGXS=1 install
/bin/mkdir -p '/usr/local/pgsql/lib'
/bin/mkdir -p '/usr/local/pgsql/share/extension'
/bin/sh /usr/local/pgsql/lib/pgxs/src/makefiles/../../config/install-sh -c -m 755  mysql_fdw.so '/usr/local/pgsql/lib/mysql_fdw.so'
/bin/sh /usr/local/pgsql/lib/pgxs/src/makefiles/../../config/install-sh -c -m 644 ./mysql_fdw.control '/usr/local/pgsql/share/extension/'
/bin/sh /usr/local/pgsql/lib/pgxs/src/makefiles/../../config/install-sh -c -m 644 ./mysql_fdw--1.0.sql  '/usr/local/pgsql/share/extension/'
[root@server mysql_fdw-1.0.1]#

检查一下 mysql_fdw.so文件，是否出现在 /usr/local/pgsql/lib 目录下。

然后，分别启动mysql和 postgresql：

[root@server ~]# mysqld_safe &
[1] 3223
[root@server ~]# 130918 09:38:14 mysqld_safe Logging to '/usr/local/mysql/data/server.gao.err'.
130918 09:38:14 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data
 

[root@server ~]# su - postgres
[postgres@server ~]$ pwd
/home/postgres
[postgres@server ~]$ cd /usr/local/pgsql
[postgres@server pgsql]$ ./bin/pg_ctl -D ./data start
server starting
[postgres@server pgsql]$ LOG:  database system was shut down at 2013-09-13 13:36:47 CST
LOG:  autovacuum launcher started
LOG:  database system is ready to accept connections

在PostgreSQL端，建立FDW:

[postgres@server pgsql]$ ./bin/psql
psql (9.1.2)
Type "help" for help.

postgres=# CREATE EXTENSION mysql_fdw;
ERROR:  extension "mysql_fdw" already exists
postgres=# CREATE SERVER mysql_svr FOREIGN DATA WRAPPER mysql_fdw OPTIONS (address '127.0.0.1', port '3306');
CREATE SERVER

postgres=# CREATE FOREIGN TABLE example (id INT,data VARCHAR(100) ) SERVER mysql_svr
postgres-#     OPTIONS (table 'mysql.example');
CREATE FOREIGN TABLE
postgres=# 
postgres=# CREATE USER MAPPING FOR PUBLIC SERVER mysql_svr OPTIONS (username 'usrabc', password 'usrabc');
CREATE USER MAPPING
postgres=# 
postgres=# select * from example;
ERROR:  failed to connect to MySQL: Access denied for user 'usrabc'@'localhost' (using password: YES)
postgres=# 
postgres=# select * from example;
 id | data 
----+------
(0 rows)

postgres=#