与postgresql_fdw功能类似，KINGBASE_FDW 是一种外部访问接口，它可以被用来访问存储在外部的数据。想要使用fdw访问数据需要先确保：网络通，数据库访问配置(pg_hba,conf)正常，同时远端数据库的用户必须有表的相关权限。
一、远程数据库
远程数据库 IP: 142 。创建用户及测试数据：
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create role user_remote with login;
alter role user_remote with password 'user_remote';
create schema user_remote authorization user_remote;
\c test user_remote
create table t1(id integer,name varchar(9));
insert into t1 values(1,'a'),(2,'b');
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二、本地数据库
本地数据库 IP: 143
1、创建扩展 kingbase_fdw
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\c test system
create role user_local with login;
alter role user_local with password 'user_local';
create schema user_local authorization user_local;
create extension kingbase_fdw;
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扩展创建完成后，pg_foreign_data_wrapper 有如下一行：
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test=# select * from pg_foreign_data_wrapper where fdwname='kingbase_fdw';
oid | fdwname | fdwowner | fdwhandler | fdwvalidator | fdwacl | fdwoptions
16495 | kingbase_fdw | 10 | 16493 | 16494 | |
(1 row)
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2、create server
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create server srv_42 foreign data wrapper kingbase_fdw options(host '192.168.237.42',port '54321',dbname 'test');
grant usage on foreign server srv_42 to user_local;
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注意：必须将 Server 授权给用户，否则用户在创建外部表时，会报“ERROR: permission denied for foreign server srv_42” 错误。创建完server后，在sys_foreign_server 会有如下一条：
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test=> select * from sys_foreign_server where srvname='srv_42';
oid | srvname | srvowner | srvfdw | srvtype | srvversion | srvacl | srvoptions
16502 | srv_42 | 10 | 16495 | | | {system=U/system,user_local=U/system} | {host=192.168.237.42,port=54321,dbname=test}
(1 row)
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3、创建user mapping
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create user mapping for user_local server srv_42 options(user 'user_remote',password 'user_remote');
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创建后，在pg_user_mappings 会有一条记录：
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test=> select * from pg_user_mappings where srvname='srv_42';
umid | srvid | srvname | umuser | usename | umoptions
16503 | 16502 | srv_42 | 16500 | user_local | {user=user_remote,password=user_remote}
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4、创建外部表
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create foreign table ft_t1 (
id integer ,
name varchar(9)
) server srv_42 options (schema_name 'user_remote',table_name 't1');
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5、访问测试
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test=> \d
List of relations
Schema | Name | Type | Owner
user_local | ft_t1 | foreign table | user_local
(1 row)
test=> select * from ft_t1;
id | name
1 | a
2 | b
(2 rows)
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6、选择导入远程的整个schema
可以将远程schema下的所有表及视图通过import 方式导入，避免逐表创建。
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test=> import foreign schema user_remote from server srv_42 into user_local;
IMPORT FOREIGN SCHEMA
test=> \d
List of relations
Schema | Name | Type | Owner
user_local | t1 | foreign table | user_local
user_local | t2 | foreign table | user_local
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