PostgreSQL的DBLink使用

習慣了Oracle的Dblink帶來的便捷，咱們來看一下PostgreSQL的DBLINK，該工具須要編譯安裝一下使用，倒也不是很複雜。 DB版本：9.1.3 1.編譯安裝

[postgres@localhost  dblink]$ pwd
/home/postgres/postgresql-9.1.3/contrib/dblink
[postgres@localhost  dblink]$ make
make -C ../../src/interfaces/libpq all
make[1]: Entering directory `/home/postgres/postgresql-9.1.3/src/interfaces/libpq'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `/home/postgres/postgresql-9.1.3/src/interfaces/libpq'
[postgres@localhost  dblink]$ make install
make -C ../../src/interfaces/libpq all
make[1]: Entering directory `/home/postgres/postgresql-9.1.3/src/interfaces/libpq'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `/home/postgres/postgresql-9.1.3/src/interfaces/libpq'
/bin/mkdir -p '/home/postgres/lib'
/bin/mkdir -p '/home/postgres/share/extension'
/bin/sh ../../config/install-sh -c -m 755  dblink.so '/home/postgres/lib/dblink.so'
/bin/sh ../../config/install-sh -c -m 644 ./dblink.control '/home/postgres/share/extension/'
/bin/sh ../../config/install-sh -c -m 644 ./dblink--1.0.sql ./dblink--unpackaged--1.0.sql  '/home/postgres/share/extension/'
[postgres@localhost  dblink]$

咱們能夠在$PGHOME/share/extension下看到3個dblink文件在$PGHOME/lib下也生成一個dblink.so的動態文件 2.建立DBLINK的擴展

[postgres@localhost  dblink]$ psql -d test -U postgres
psql (8.4.9, server 9.1.3)
WARNING: psql version 8.4, server version 9.1.
         Some psql features might not work.
Type "help" for help.

test=# create extension dblink;
CREATE EXTENSION
test=#

3.查看當前數據庫裏的擴展包

test=# select extname,extversion from pg_extension;
  extname  | extversion 
-----------+------------
 plpgsql   | 1.0
 tablefunc | 1.0
 dblink    | 1.0
(3 rows)

4.工具欄中得體現




5.DBLINK使用 a.數據庫中狀況以下：

[postgres@localhost  etc]$ psql
psql (8.4.9, server 9.1.3)
WARNING: psql version 8.4, server version 9.1.
         Some psql features might not work.
Type "help" for help.

postgres=# \l
                              List of databases
   Name    |  Owner   | Encoding | Collation | Ctype |   Access privileges   
-----------+----------+----------+-----------+-------+-----------------------
 kenyon    | postgres | UTF8     | C         | C     | 
 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     | 
(5 rows)

postgres=# \c kenyon
psql (8.4.9, server 9.1.3)
WARNING: psql version 8.4, server version 9.1.
         Some psql features might not work.
You are now connected to database "kenyon".
kenyon=# select * from test;
 id |       name        
----+-------------------
  1 | kenyon
  2 | God in your heart
(2 rows)

b.創建dblink鏈接

test=# select dblink_connect('kenyon_dblink','dbname=kenyon host=localhost port=1949 user=postgres password=postgres');
 dblink_connect 
----------------
 OK
(1 row)

c.使用

test=# select * from dblink('kenyon_dblink','select * from test') as  t1 (id integer,name varchar);)
 id |       name        
----+-------------------
  1 | kenyon
  2 | God in your heart
(2 rows)

涉及PG的dblink函數見上面的圖，下面不介紹。
簡單使用的總結
好處：能夠跨庫進行Select，簡化了很多工做
劣處：感受還不是很完善，使用上比Oracle的要麻煩一點,最後的查詢表t1結果集取決於前面查詢test的結果集。

PS：在編譯dblink的時候，發生了一些波折，以前由於安裝的源碼文件被動過，編譯安裝後建立extension時一直報load dblink.so文件失敗。後來在德哥的幫助下，從新安裝DB，不變更文件狀況下正常生成。這也提了個醒，安裝DB成功後無論源文件，仍是安裝文件等就不要去動了，前期要有一套規範的DB安裝設計。
德哥的BLOG： http://blog.163.com/digoal@126/blog/static/163877040201232692431920/