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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 |
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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