要迁移Mysql的数据到PostgreSQL上来，有很多的办法，比如一些工具navicat,jmyetl等，但通常是要收费，而且效率和稳定性不一定好，最保守的办法是自己写一些脚本，当然也有一些开源的工具，比如要介绍的mysql_fdw，使用时本地需要建mysql软件和postgresql数据库，下面的测试例子是mysql和pg装在一起的。

mysql_fdw是一款基于BSD协议的开源工具，目前还不是postgresql内置，最新版本是1.0.1。

一、环境
CentOS 6.3
PostgreSQL 9.3.4
Host 10.1.11.73

二、Mysql的数据准备

mysql> create database db_kenyon;Query OK, 1 row affected (0.01 sec)mysql> create table tbl_kenyon(id int,vname varchar(48));Query OK, 0 rows affected (0.00 sec)mysql> insert into tbl_kenyon values(1,'test');Query OK, 1 row affected (0.00 sec)mysql> insert into tbl_kenyon values(2,'kenyon');Query OK, 1 row affected (0.00 sec)mysql> insert into tbl_kenyon values(null,'it/'s null');Query OK, 1 row affected (0.00 sec)mysql> insert into tbl_kenyon values(4,null);Query OK, 1 row affected (0.01 sec)mysql> select * from tbl_kenyon;+------+-----------+| id | vname |+------+-----------+| 1 | test || 2 | kenyon || NULL | it's null || 4 | NULL |+------+-----------+4 rows in set (0.00 sec)mysql> grant select on db_kenyon.tbl_kenyon to 'usr_kenyon'@'%' identified by '123456';Query OK, 0 rows affected (0.00 sec)mysql> flush privileges;Query OK, 0 rows affected (0.00 sec)mysql> select host,user,password from mysql.user;+-----------+------------+-------------------------------------------+| host | user | password |+-----------+------------+-------------------------------------------+| localhost | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || db1 | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || 127.0.0.1 | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || ::1 | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 || % | usr_kenyon | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |+-----------+------------+-------------------------------------------+5 rows in set (0.00 sec)

三、 安装使用 mysql_fdw

下载地址： http://pgxn.org/dist/mysql_fdw/
安装时使用postgres用户，参考README，有两步
make USE_PGXS=1
make USE_PGXS=1 install
安装完可能会有的异常，ERROR: could not load library "/home/postgres/lib/mysql_fdw.so": libmysqlclient.so.18: cannot open shared object file: No such file or directory 将mysql下的libmysqlclient.so.18文件拷贝到/home/postgres/lib下面或者做个软连接就可以了

1.创建extension扩展

postgres=# create extension mysql_fdw ;CREATE EXTENSION

2.创建server

postgres=# CREATE SERVER mysql_svr FOREIGN DATA WRAPPER mysql_fdw OPTIONS (address '10.1.11.73', port '3306');CREATE SERVER

3.创建一个或多个外部表(foreign table)

postgres=# CREATE FOREIGN TABLE pg_mysql_tbl1 (id integer, name text) SERVER mysql_svr OPTIONS (table 'db_kenyon.tbl_kenyon');CREATE FOREIGN TABLEpostgres=# CREATE FOREIGN TABLE pg_mysql_tbl2 ( id integer, vname text) SERVER mysql_svr OPTIONS (query 'SELECT id, vname FROM db_kenyon.tbl_kenyon WHERE id<>2;');CREATE FOREIGN TABLE

4.创建PostgreSQL的fdw查询用户，pg_hba配置略

postgres=# create user u_select ENCRYPTED PASSWORD '123456';CREATE ROLE

5.创建用户匹配关系(user mapping),用户为远程mysql的用户密码

CREATE USER MAPPING FOR u_select SERVER mysql_svr OPTIONS (username 'usr_kenyon', password '123456');

6.查询数据，需要u_select登录，不然会报user mapping not found

postgres=> select * from pg_mysql_tbl1 ; id | name ----+----------- 1 | test 2 | kenyon | it's null 4 | (4 rows)postgres=> select * from pg_mysql_tbl2; id | vname ----+------- 1 | test 4 | (2 rows)

四、删除扩展

postgres=# drop foreign table pg_mysql_tbl1;DROP FOREIGN TABLEpostgres=# drop foreign table pg_mysql_tbl2;DROP FOREIGN TABLEpostgres=# drop user mapping for u_select server mysql_svr ;DROP USER MAPPINGpostgres=# drop server mysql_svr ;DROP SERVERpostgres=# drop extension mysql_fdw ;DROP EXTENSION

五、总结
1.这个工具在ETL迁移Mysql到postgresql时比较有用，跨平台，跨数据库，而且简单方便
2.目前该工具还不是内置版本，引起的风险要注意，比如mysql和pg库端表字段后类型不一样，会产生乱码


六、参考：
1.http://pgxn.org/dist/mysql_fdw/
2.http://francs3.blog.163.com/blog/static/40576727201111211324599/?suggestedreading

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