PostgreSQL的dblink扩展模块使用

CREATE EXTENSION IF NOT EXISTS dblink;
###如果已经有，可以在 pg 扩展表查到
SELECT * FROM pg_extension WHERE extname = 'dblink'; 
或使用\dx 
postgres=# \dx
                                                 已安装扩展列表
        名称        | 版本 |  架构模式  |                                  描述
--------------------+------+------------+------------------------------------------------------------------------
 adminpack          | 2.1  | pg_catalog | administrative functions for PostgreSQL
 dblink             | 1.2  | postgres   | connect to other PostgreSQL databases from within a database
 oracle_fdw         | 1.2  | postgres   | foreign data wrapper for Oracle access
 pg_stat_statements | 1.9  | postgres   | track planning and execution statistics of all SQL statements executed
 plpgsql            | 1.0  | pg_catalog | PL/pgSQL procedural language

SELECT dblink_connect('local_connect','hostaddr=127.0.0.1 port=5432 dbname=xxxx user=xxxx password=xxxx') as dev;
解释：
'local_connect'  是我自定义的连接的名称
hostaddr=127.0.0.1  表示是本机地址
port=5432  表示使用5432端口，自行设置
dbname  表示要访问的数据库的名称
user，password分别表示用户名和密码，根据自己配置的用户名密码更改

如：
postgres=# SELECT dblink_connect('local_connect','hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr') as dev;

 dev
-----

 OK
(1 行记录)

-- 查询所有已链接的dblink
select dblink_get_connections();

postgres=# select dblink_get_connections();
 dblink_get_connections
------------------------
 {local_connect}
(1 行记录)

--跨库查询
SELECT num,id FROM dblink('local_connect','select num,id from hr.demotable') as t(num numeric,id integer);
SELECT * FROM dblink('local_connect','select num,id from hr.demotable') as t(num numeric,id integer);
SELECT * FROM dblink('local_connect','select * from hr.demotable') as t(num numeric,id integer);

--跨库查询写入
insert into t_dblink
select * from dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable where id<1000') as t(num numeric,id integer);

####使用 dblink 函数从远程数据库获取数据。 local_connect是预先配置好的远程数据库连接名
####dblink 中查询语句被引号括起来，如果查询语句本身有引号，需要多写一个引号做转义
####AS t()表示dblink返回的结果集定义了一个别名't'，并指定了每个列的数据类型

-- 关闭远程连接
###在PostgreSQL中dblink是会话级别；会话断开即dblink也关闭。当然也可以在会话中手动关闭
SELECT dblink_disconnect('local_connect');

-- 查询所有已链接的dblink
select dblink_get_connections();

--直接写 dblink 方式，预先配置好的到远程数据库的连接名 
SELECT * FROM dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable') as t(num numeric,id integer);


create table t_dblink as select * from dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable where 1=2') as t(num numeric,id integer);

insert into t_dblink
select * from dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable where id<1000') as t(num numeric,id integer);

explain analyze with t_temp as (select * from dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable where id<1000') as t(num numeric,id integer)) 
select a.num,a.id from t_dblink a,t_temp b where a.id=b.id;

postgres=# create temp table t_dblink as SELECT * FROM dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable') as t(num numeric,id integer);
SELECT 1000000
postgres=# select * from t_dblink;
...........

--退出后重新进去临时表不存在
postgres=# select * from t_dblink;
错误:  关系 "t_dblink" 不存在
第1行select * from t_dblink;

postgres=# create view  v_dblink as SELECT * FROM dblink('hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr','select * from hr.demotable') as t(num numeric,id integer);
CREATE VIEW
postgres=# select * from v_dblink;
................
--退出后，重新执行
postgres=# select * from v_dblink;

SELECT dblink_connect('local_connect','hostaddr=127.0.0.1 port=5432 dbname=hrdb user=hr password=hr') as dev;
SELECT dblink_exec('local_connect', 'create table aa(id int,name varchar(50))');
SELECT dblink_exec('local_connect', 'drop table aa');
SELECT dblink_exec('local_connect', 'insert into hr.t values (1011102,8999,''hello'',''2048-10-09''::date)');
SELECT dblink_exec('local_connect', 'delete from  hr.t values where id=1011102');