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PostgreSQL跨库访问有3种方法：Schema，dblink，postgres_fdw。

方法A：在PG上建立不同SCHEMA，将数据和存储过程分别放到不同的schema上，经过权限管理后进行访问。

方法A的示例如下：

测试1（测试postgres超级用户对不同schema下对象的访问）

查看当前数据库中的schema

 postgres=# \dn

 List of schemas

 Name | Owner

-------------------+---------

dbms_job_procedure | postgres pgagent | postgres

 postgres | postgres

 public | postgres

 (4 rows)

（当前连接数据库的用户为postgres）

postgres=# select user;

user

----------

postgres

 (1 row)

创建名为test1的schema

 postgres=# create schema test1;

 CREATE SCHEMA

创建模式test1下的对象，表ticket1

 postgres=# create table test1.ticket1(id int);

 CREATE TABLE

可以看到并没有我们之前建立的表

 postgres=# \d

List of relations

 Schema | Name | Type | Owner

-------------------------+---------

public | dept | table | postgres

 public | emp | table | postgres

 public | jobhist | table | postgres

 public | next_empno | sequence | postgres

 public | salesemp | view | postgres

 (5 rows)

在对象前加schema，postgres用户可以访问ticket1表

postgres=# select * from test1.ticket1;

id

-------------------------------------------------

(0 rows)

查看模式 搜索路径

 postgres=# show search_path ;

 search_path

----------------

"$user",public

 (1 row)

把创建的模式test1添加到模式搜索路径

postgres=# set search_path to "$user",public,test1;

 SET

 postgres=# show search_path ;

 search_path

------------------------

"$user", public, test1

 (1 row)

 为了访问方便，在搜索路径中添加schema对象之后既可以看到该模式下的表，也可以直接进行搜索，而不用添加schema前缀。（这里因为是超级用户，所以不用给postgres赋权，如果是普通用户，想要访问，需要赋权）

 postgres=# \d

List of relations

 Schema | Name | Type | Owner

-------------------------+---------

public | dept | table | postgres

 public | emp | table | postgres

 public | jobhist | table | postgres

 public | next_empno | sequence | postgres

 public | salesemp | view | postgres

 test1 | ticket1 | table | postgres

 (6 rows)

 postgres=# select * from ticket1;

 id

--------------------------------------------

(0 rows)

 测试2：

 在postgres用户下建立名为test2的schema

 postgres=# create schema test2;

 CREATE SCHEMA

 postgres=# create table test2.ticket2(id int);

 CREATE TABLE

建立两个普通用户

 postgres=# create role test1 login password '123';

 CREATE ROLE

 postgres=# create role test2 login password '123';

 CREATE ROLE

普通用户连接数据库

 postgres=# \c postgres test2;

 Password for user test2:

You are now connected to database "postgres" as user "test2".

 postgres=> \d

 List of relations

 Schema | Name | Type | Owner

-------------------------+---------

public | dept | table | postgres

 public | emp | table | postgres

 public | jobhist | table | postgres

 public | next_empno | sequence | postgres

 public | salesemp | view | postgres

 (5 rows)

postgres=> show search_path ;

 search_path

----------------

"$user",public

 (1 row)

postgres=> set search_path to "$user",public,test1;

 SET

postgres=> \d

 List of relations

 Schema | Name | Type | Owner

-------------------------+---------

public | dept | table | postgres

 public | emp | table | postgres

 public | jobhist | table | postgres

 public | next_empno | sequence | postgres

 public | salesemp | view | postgres

 test1 | ticket1 | table | postgres

 test2 | ticket2 | table | postgres

 (11 rows)

 可以看到test2用户模式下的ticket2表，但是访问时权限不足。

 postgres=> select * from test2.ticket2;

 ERROR: permission denied for relation ticket2

 postgres=> select * from ticket2;

ERROR: permission denied for relation ticket2

 通过postgres超级用户赋予权限，即可访问

 postgres=# grant select on all tables in schema test2 to test1;

 GRANT

 postgres=> select * from test2.ticket2;

 id

---------------------------------------------------

(0 rows)

postgres=> select * from ticket2;

id

---------------------------------------------------

(0 rows)

方法B：通过dblink实现跨库访问

方法B测试示例如下：

环境：本地：192.168.56.88 数据库：postgres

 远程：192.168.56.99 数据库：test

 

PostgreSQL通过dblink实现跨库访问

测试1：在同一个实例下分别建立两个数据库，通过dblink 实现跨库访问

postgres=# create database test;

CREATE DATABASE

postgres=# \l

                             List of databases

   Name    |  Owner   | Encoding | Collate | Ctype |   Access privileges  

-----------+----------+----------+---------+-------+-----------------------

 postgres  | postgres | UTF8     | C       | C     |

 template0 | postgres | UTF8     | C       | C     | =c/postgres          +

           |          |          |         |       | postgres=CTc/postgres

 template1 | postgres | UTF8     | C       | C     | =c/postgres          +

           |          |          |         |       | postgres=CTc/postgres

 test      | postgres | UTF8     | C       | C     |

(4 rows)

postgres=# \c test

You are now connected to database "test" as user "postgres".

test=# create table test(id int);

CREATE TABLE

test=# \d

        List of relations

 Schema | Name | Type  |  Owner  

--------+------+-------+----------

 public | test | table | postgres

(1 row)

test=# create table test2(id int);

CREATE TABLE

test=# insert into test values ('1111');

INSERT 0 1

test=# \c postgres

You are now connected to database "postgres" as user "postgres".

在postgres数据库中建立dblink连接到test数据库

postgres=# create extension dblink;

CREATE EXTENSION

postgres=# select * from pg_extension;

 extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition

---------+----------+--------------+----------------+------------+-----------+--------------

 plpgsql |       10 |           11 | f              | 1.0        |           |

 dblink  |       10 |         2200 | t              | 1.1        |           |

(2 rows)

postgres=# select dblink_connect('test_dblink','dbname=test host=localhost port=5432 user=postgres password=postgres');

 dblink_connect

----------------

 OK

(1 row)

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

  id 

------

 1111

(1 row)

通过建立dblink，在postgres数据库可以很容易的访问到test数据库中的数据。

为了访问test数据库中的数据方便，我们可以建立一个视图，操作如下，我们只需要查询视图中的内容即可。

postgres=# CREATE VIEW testdb_dblink AS  

postgres-# SELECT * FROM dblink('hostaddr=127.0.0.1 port=5432 dbname=test user=postgres password=postgres', 'SELECT * From test') AS t(id int);

CREATE VIEW

postgres=# \d

                  List of relations

 Schema |          Name           | Type  |  Owner  

--------+-------------------------+-------+----------

 public | ptest1                  | table | postgres

 public | ptest2                  | table | postgres

 public | remote_people_user_name | view  | postgres

 public | testdb_dblink           | view  | postgres

(4 rows)

postgres=# select * from testdb_dblink ;

  id 

------

 1111

(1 row)

测试2：

在两个实例下分别创建数据库，然后通过dblink实现垮库访问。

实例1：

首先需要配置下路由配置，添加一行命令-A INPUT -s 192.168.0.0/16 -j ACCEPT

[root@darry etc]# vi /etc/sysconfig/iptables

...

添加-A INPUT -s 192.168.0.0/16 -j ACCEPT  即允许192.168.0.0的网段访问

....

[root@darry etc]# service iptables reload

iptables: Trying to reload firewall rules:                 [  OK  ]

在IP为192.168.56.88（本地）的postgres数据库中建立extension

postgres=# create extension dblink;

CREATE EXTENSION

postgres=# select  * from pg_extension;

 extname | extowner | extnamespace | extrelocatable | extversion | extconfig | extcondition

---------+----------+--------------+----------------+------------+-----------+--------------

 plpgsql |       10 |           11 | f              | 1.0        |           |

 dblink  |       10 |         2200 | t              | 1.1        |           |

(2 rows)

建立dblink 访问IP为192.168.56.99（远程）数据库

postgres=# select dblink_connect('test_dblink','dbname=test host=192.168.56.99 port=5432 user=postgres password=postgres');

 dblink_connect

----------------

 OK

(1 row)

 

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

  id 

------

 1111

(1 row)

跨库事务测试

连接远程数据库

postgres=# select dblink_connect('test_dblink','dbname=test host=192.168.56.99 port=5432 user=postgres password=postgres');

 dblink_connect

----------------

 OK

(1 row)

在远程服务器上开始一个事务

postgres=# select dblink_exec('test_dblink','begin;');

 dblink_exec

-------------

 BEGIN

(1 row)

插入一条数据

postgres=# select dblink_exec('test_dblink','insert into test values(7777);');

 dblink_exec

-------------

 INSERT 0 1

(1 row)

经查看远程服务器上已经插入一条数据

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

  id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

  7777

(11 rows)

在远程数据库中查看未发现数据，因为事务未提交

test=# select * from test;

  id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

在本地数据库中提交远程连接数据库中的事务

postgres=# select dblink_exec('test_dblink','commit;');

 dblink_exec

-------------

 COMMIT

(1 row)

再次查看

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

  id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

  7777

远程数据库中也存在

test=# select * from test;

  id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

  7777

若换成将commit替换成rollback则插入取消

postgres=# select dblink_exec('test_dblink','begin;');

 dblink_exec

-------------

 BEGIN

(1 row)

postgres=# select dblink_exec('test_dblink','insert into test values(99999);');

 dblink_exec

-------------

 INSERT 0 1

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

  id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

  7777

 99999

执行回滚操作

postgres=# select dblink_exec('test_dblink','rollback;');

 dblink_exec

-------------

 ROLLBACK

(1 row)

经查看回滚之后，不记录之前插入的数据

postgres=# select * from dblink('test_dblink','select * from test') as t1(id int);

   id  

-------

  1111

  2222

  3333

  4444

  6666

 33333

  7777

方法C：通过postgres_fdw实现跨库访问

环境：本地：192.168.0.14，远程：192.168.0.17，PG：9.3.9两台机器的测试用户及数据库均为：test,test

1.在本地数据库中创建postgres_fdw extension.

[postgres@minion1 bin]$ ./psql test test

psql (9.3.9)

Type "help" for help.

test=# \c test test

You are now connected to database "test" as user "test".

test=# create extension postgres_fdw ;

CREATE EXTENSION

2.在远程数据库上生成测试数据 :

[postgres@minion4 bin]$ ./psql test test

psql (9.3.9)

Type "help" for help.

test=# CREATE TYPE user_enum AS ENUM ('foo', 'bar', 'buz');

CREATE TYPE

test=# \dT

        List of data types

 Schema |   Name    | Description

--------+-----------+-------------

 public | user_enum |

(1 row)

 

test=# select oid from pg_type where typname='user_enum';

  oid 

-------

 16902

(1 row)

test=# CREATE SCHEMA test;

CREATE SCHEMA

test=# CREATE TABLE test.test1 (

test(# c1 int NOT NULL,

test(# c2 int NOT NULL,

test(# c3 text,

test(# c4 timestamptz,

test(# c5 timestamp,

test(# c6 varchar(10),

test(# c7 char(10),

test(# c8 user_enum,

test(# CONSTRAINT t1_pkey PRIMARY KEY (c1)

test(# );

CREATE TABLE

test=# CREATE TABLE test.test2 (

test(# c1 int NOT NULL,

test(# c2 text,

test(# CONSTRAINT t2_pkey PRIMARY KEY (c1)

test(# );

CREATE TABLE

test=# INSERT INTO test.test1

test-# SELECT id,

test-#        id % 10,

test-#        to_char(id, 'FM00000'),

test-#        '1970-01-01'::timestamptz + ((id % 100) || ' days')::interval,

test-#        '1970-01-01'::timestamp + ((id % 100) || ' days')::interval,

test-#        id % 10,

test-#        id % 10,

test-#        'foo'::user_enum

test-# FROM generate_series(1, 1000) id;

INSERT 0 1000

test=# INSERT INTO test.test2

test-# SELECT id,

test-#        'AAA' || to_char(id, 'FM000')

test-# FROM generate_series(1, 100) id;

INSERT 0 100

test=# analyze test.test1;

ANALYZE

test=# analyze test.test2;

ANALYZE

3.在本地数据库中创建server

test=# CREATE SERVER s1 FOREIGN DATA WRAPPER postgres_fdw;

CREATE SERVER

test=# select * from pg_foreign_server ;

 srvname | srvowner | srvfdw | srvtype | srvversion | srvacl | srvoptions

---------+----------+--------+---------+------------+--------+------------

 s1      |    17444 |  17449 |         |            |        |

(1 row)

test=# alter server s1 options ( add hostaddr '192.168.0.17', add port '5432', add dbname 'test');

ALTER SERVER

4.SERVER赋权 :

test=# grant usage on foreign server s1 to test;

GRANT

test=# select * from pg_foreign_server ;

 srvname | srvowner | srvfdw | srvtype | srvversion |    srvacl     |                  srvoptions   

              

---------+----------+--------+---------+------------+---------------+--------------------------------

---------------

 s1      |    17444 |  17449 |         |            | {test=U/test} | {hostaddr=192.168.0.17,port=543

2,dbname=test}

(1 row)

5.在本地数据库中创建user mapping : 

test=# create user mapping for test server s1 options(user 'test',password 'test');

CREATE USER MAPPING

6.在本地数据库中创建foreign table

test=# CREATE TYPE user_enum AS ENUM ('foo', 'bar', 'buz');

CREATE TYPE

test=# \dT

        List of data types

 Schema |   Name    | Description

--------+-----------+-------------

 public | user_enum |

(1 row)

 

test=# select oid from pg_type where typname='user_enum';

  oid 

-------

 17453

(1 row)

test=# CREATE FOREIGN TABLE ft1 (

test(#  c0 int,

test(#  c1 int NOT NULL,

test(#  c2 int NOT NULL,

test(#  c3 text,

test(#  c4 timestamptz,

test(#  c5 timestamp,

test(#  c6 varchar(10),

test(#  c7 char(10),

test(#  c8 user_enum

test(#  ) SERVER s1 options(schema_name 'test', table_name 'test1');

CREATE FOREIGN TABLE

test=# select * from ft1 limit 1;

ERROR:  column "c0" does not exist

CONTEXT:  Remote SQL command: SELECT c0, c1, c2, c3, c4, c5, c6, c7, c8 FROM test.test1

test=# alter foreign table ft1 drop column c0;

ALTER FOREIGN TABLE

test=# select * from ft1 limit 1;

 c1 | c2 |  c3   |           c4           |         c5          | c6 |     c7     | c8 

----+----+-------+------------------------+---------------------+----+------------+-----

  1 |  1 | 00001 | 1970-01-02 00:00:00+08 | 1970-01-02 00:00:00 | 1  | 1          | foo

(1 row)

test=# create foreign table ft2 (c2 text,c1 int not null) server s1 options(schema_name 'test',table_name 'test2');

CREATE FOREIGN TABLE

test=# select * from ft2 limit 1;

   c2   | c1

--------+----

 AAA001 |  1

(1 row)

test=# create foreign table ft3(c2 text,c3 int not null) server s1 options(schema_name 'test',table_name 'test2');

CREATE FOREIGN TABLE

test=# select * from ft3 limit 1;

ERROR:  column "c3" does not exist

CONTEXT:  Remote SQL command: SELECT c2, c3 FROM test.test2

test=# alter foreign table ft3 alter column c3 options (column_name 'c1');

ALTER FOREIGN TABLE

test=# select * from ft3 limit 1;

   c2   | c3

--------+----

 AAA001 |  1

(1 row)

test=# create foreign table ft4(c2 text,c3 int options (column_name 'c1') not null) server s1 options(schema_name 'test',table_name 'test2');

CREATE FOREIGN TABLE

test=# select * from ft4 limit 2;

   c2   | c3

--------+----

 AAA001 |  1

 AAA002 |  2

(2 rows)

PostgreSQL跨库访问事务测试

远程机器创建测试表

test=# create table test3(id int);

CREATE TABLE

test=# select * from test3;

 id

----

(0 rows)

本地机器测试

创建对应的外部表

test=# create foreign table ft_test3(id int) server s1 options(schema_name 'test',table_name 'test3');

CREATE FOREIGN TABLE

test=# select * from ft_test3 ;

 id

----

(0 rows)

本地机器事务测试（不提交）

test=# begin;

BEGIN

test=# insert into ft_test3 values (100);

INSERT 0 1

test=# insert into ft_test3 values (200);

INSERT 0 1

test=# insert into ft_test3 values (300);

INSERT 0 1

test=# select * from ft_test3 ;

 id 

-----

 100

 200

 300

(3 rows)

test=# rollback;

ROLLBACK

test=# select * from ft_test3 ;

 id

----

(0 rows)

本地机器事务测试（提交）

test=# begin;

BEGIN

test=# insert into ft_test3 values (1000);

INSERT 0 1

test=# insert into ft_test3 values (2000);

INSERT 0 1

test=# insert into ft_test3 values (3000);

INSERT 0 1

test=# end;

COMMIT

test=# select * from ft_test3 ;

  id 

------

 1000

 2000

 3000

(3 rows)

test=# rollback;

NOTICE:  there is no transaction in progress

ROLLBACK