postgresql添加mysql_fdw測試過程

請先確認已經安裝好mysql_fdw,如果沒有配置好點這：https://www.cnblogs.com/ohsolong/p/13041989.html

1.切換至postgres用戶，輸入密碼登錄 。注：如果安裝了postgresql系統會自動創建該用戶

 su postgres 

2.登錄postgres數據庫。注：安裝postgresql時默認生成的數據庫， 也可以登錄自己創建的數據庫，這里為了方便直接登錄默認提供的數據庫。

$ psql
psql (10.12 (Ubuntu 10.12-0ubuntu0.18.04.1))
Type "help" for help.

postgres=#

2.接下來按照官方文檔流程使用mysql_fdw,官方文檔點這：https://pgxn.org/dist/mysql_fdw/

  使用的命令說明在postgresql文檔中，點這:http://postgres.cn/docs/10/postgres-fdw.html

 第一步:加載mysql_fdw擴展

CREATE EXTENSION mysql_fdw;

第二步:創建連接外部數據庫的連接對象

CREATE SERVER mysql_server
     FOREIGN DATA WRAPPER mysql_fdw
     OPTIONS (host '127.0.0.1', port '3306');

第三步:創建用戶映射，postgresql用戶映射mysql服務器的用戶（postgresql數據庫用戶:postgres; mysql數據庫用戶:foo）

CREATE USER MAPPING FOR postgres
SERVER mysql_server
OPTIONS (username 'foo', password 'bar');　　

第四步:創建與mysql中對應的外部表。注:表名稱，列名一致，對應列數據類型可以不同但能夠轉換(依賴與數據庫本身)

CREATE FOREIGN TABLE warehouse(
     warehouse_id int,
     warehouse_name text,
     warehouse_created TIMESTAMPZ)
SERVER mysql_server
     OPTIONS (dbname 'db', table_name 'warehouse');

在postgresql中向mysql外部數據庫插入數據，發現出出錯。

postgres=# insert into warehouse values (1,'ups',now());
ERROR:  failed to connect to MySQL: Access denied for user 'foo'@'localhost' (using password: YES)

3.上面出錯的原因是我沒有安裝mysql_server，

   以及沒有在mysql中添加上面映射的 foo 用戶，

　以及沒有創建名為db的數據庫並在其中創建warehouse表，接下來進行配置。

    第一步:安裝mysql_server，啟動mysql服務，切換至root用戶登錄mysql

安裝數據庫
$ sudo apt install mysql-server

啟動數據庫
$ service mysql start

登錄mysql並創建遠程用戶
$ su root 
# mysql -uroot
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.7.30-0ubuntu0.18.04.1 (Ubuntu)
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
create user foo identified by 'bar';
Query OK, 0 rows affected (0.00 sec)

給用戶授權
mysql> grant all privileges on *.* to 'foo'@'%'identified by 'bar' with grant option;
Query OK, 0 rows affected, 1 warning (0.00 sec)

創建數據庫
mysql> create database db;
Query OK, 1 row affected (0.00 sec)

計入數據庫
mysql> user db;

創建表
mysql> create table warehouse( warehouse_id int, warehouse_name text, warehouse_created timestamp);
Query OK, 0 rows affected (0.03 sec)

4.在postgresql上向外表插入數據,發現沒有創建表的唯一索引

postgres=# insert into warehouse values (1, 'ups', now());
ERROR:  first column of remote table must be unique for INSERT/UPDATE/DELETE operation　　

mysql表中創建唯一索引

mysql> create unique index warehouse_index on warehouse(warehouse_id);

5.最后測試

 postgresql插入數據 mysql中查詢成功（INSERT INTO）　

postgres=# insert into warehouse values (1,'ups',now());
INSERT 0 1
postgres=# 

mysql> select * from warehouse;
+--------------+----------------+---------------------+
| warehouse_id | warehouse_name | warehouse_created   |
+--------------+----------------+---------------------+
|            1 | ups            | 2020-06-04 15:41:51 |
+--------------+----------------+---------------------+
1 row in set (0.00 sec)

mysql> 

postgresql更新數據 mysql中查詢成功（UPDATE）　　

postgres=# update warehouse set warehouse_name = 'ups_new' ,warehouse_created = now() where warehouse_id=1;
UPDATE 1
postgres=# 

mysql> select * from warehouse;
+--------------+----------------+---------------------+
| warehouse_id | warehouse_name | warehouse_created   |
+--------------+----------------+---------------------+
|            1 | ups_new        | 2020-06-04 16:53:01 |
+--------------+----------------+---------------------+
1 row in set (0.00 sec)

mysql> 

postgresql刪除數據 mysql中查詢成功（DELETE）　　

postgres=# delete from warehouse where warehouse_id=1;
DELETE 1
postgres=# 

mysql> select * from warehouse;
Empty set (0.00 sec)

mysql> 

 done

第一次使用外部數據功能，看了一些文檔，總的來說不難。吧整個流程整理了一下，以后用到有跡可循，也希望能夠幫助到大家。