postgresql/contrib/dblink
Bruce Momjian 7aac048b59 Attached is a patch to deal with the ones that I missed the first time
around.  I tested this patch under Cygwin and Linux.

Note that I only changed dblink's Makefile in the most minimal way
to fix the link problem under Cygwin (i.e., use the link rule from
Makefile.shlib instead).  dblink's Makefile should probably be further
patched to be consistent with the other PostgreSQL Makefiles.

Jason Tishler
2001-06-20 00:04:44 +00:00
..
dblink.c
dblink.h
dblink.sql.in
Makefile Attached is a patch to deal with the ones that I missed the first time 2001-06-20 00:04:44 +00:00
README.dblink

/*
 * dblink
 *
 * Functions returning results from a remote database
 *
 * Copyright (c) Joseph Conway <joe.conway@mail.com>, 2001;
 * 
 * Permission to use, copy, modify, and distribute this software and its
 * documentation for any purpose, without fee, and without a written agreement
 * is hereby granted, provided that the above copyright notice and this
 * paragraph and the following two paragraphs appear in all copies.
 * 
 * IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
 * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
 * ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
 * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 *
 */


Version 0.3 (14 June, 2001):
  Function to test returning data set from remote database
  Tested under Linux (Red Hat 6.2 and 7.0) and PostgreSQL 7.1 and 7.2devel

Release Notes:

  Version 0.3
    - fixed dblink invalid pointer causing corrupt elog message
    - fixed dblink_tok improper handling of null results
    - fixed examples in README.dblink

  Version 0.2
    - initial release    

Installation:
  Place these files in a directory called 'dblink' under 'contrib' in the PostgreSQL source tree. Then run:

    make
    make install

  You can use dblink.sql to create the functions in your database of choice, e.g.

    psql -U postgres template1 < dblink.sql

  installs following functions into database template1:

     dblink() - returns a pointer to results from remote query
     dblink_tok() - extracts and returns individual field results

Documentation
==================================================================
Name

dblink -- Returns a pointer to a data set from a remote database

Synopsis

dblink(text connstr, text sql)

Inputs

  connstr

    standard libpq format connection srting, 
    e.g. "hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd"

  sql

    sql statement that you wish to execute on the remote host
    e.g. "select * from pg_class"

Outputs

  Returns setof int (pointer)

Example usage

  select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd','select f1, f2 from mytable');


==================================================================

Name

dblink_tok -- Returns individual select field results from a dblink remote query

Synopsis

dblink_tok(int pointer, int fnumber)

Inputs

  pointer

    a pointer returned by a call to dblink()

  fnumber

    the ordinal position (zero based) of the field to be returned from the dblink result set

Outputs

  Returns text

Example usage

  select dblink_tok(t1.dblink_p,0) as f1, dblink_tok(t1.dblink_p,1) as f2
  from (select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
                     ,'select f1, f2 from mytable') as dblink_p) as t1;


==================================================================

NOTE: If you need to provide selection criteria in a WHERE clause, it is necessary
to 'fake' a UNION, e.g.

  select
     dblink_tok(t1.dblink_p,0) as f1
    ,dblink_tok(t1.dblink_p,1) as f2
  from
   (
    select dblink(
                   'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
                  ,'select f1, f2 from mytable'
                 ) as dblink_p
    union all
    select null where false
   ) as t1
  where
    dblink_tok(t1.dblink_p,0) = 'mycriteria';

in order to work around an issue with the query optimizer. A more convenient way to approach
this problem is to create a view:

  create view myremotetable as
  select
     dblink_tok(t1.dblink_p,0) as f1
    ,dblink_tok(t1.dblink_p,1) as f2
  from
   (
    select dblink(
                   'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
                  ,'select f1, f2 from mytable'
                 ) as dblink_p
    union all
    select null where false
   ) as t1;

Then you can simply write:

   select f1,f2 from myremotetable where f1 = 'mycriteria';

==================================================================

-- Joe Conway