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/*
* 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
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