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dblink.c | ||
dblink.h | ||
dblink.sql.in | ||
Makefile | ||
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