158 lines
4.2 KiB
Plaintext
158 lines
4.2 KiB
Plaintext
/*
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* dblink
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*
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* Functions returning results from a remote database
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*
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* Copyright (c) Joseph Conway <joe.conway@mail.com>, 2001;
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*
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* Permission to use, copy, modify, and distribute this software and its
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* documentation for any purpose, without fee, and without a written agreement
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* is hereby granted, provided that the above copyright notice and this
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* paragraph and the following two paragraphs appear in all copies.
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*
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* IN NO EVENT SHALL THE AUTHOR OR DISTRIBUTORS BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
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* LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
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* DOCUMENTATION, EVEN IF THE AUTHOR OR DISTRIBUTORS HAVE BEEN ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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* THE AUTHOR AND DISTRIBUTORS SPECIFICALLY DISCLAIMS ANY WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE AUTHOR AND DISTRIBUTORS HAS NO OBLIGATIONS TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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*/
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Version 0.2 (29 May, 2001):
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Function to test returning data set from remote database
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Tested under Linux (Red Hat 6.2 and 7.0) and PostgreSQL 7.1 and 7.2devel
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Release Notes:
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Version 0.2
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- initial release
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Installation:
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Place these files in a directory called 'dblink' under 'contrib' in the PostgreSQL source tree. Then run:
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make
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make install
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You can use dblink.sql to create the functions in your database of choice, e.g.
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psql -U postgres template1 < dblink.sql
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installs following functions into database template1:
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dblink() - returns a pointer to results from remote query
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dblink_tok() - extracts and returns individual field results
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Documentation
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==================================================================
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Name
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dblink -- Returns a pointer to a data set from a remote database
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Synopsis
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dblink(text connstr, text sql)
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Inputs
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connstr
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standard libpq format connection srting,
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e.g. "hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd"
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sql
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sql statement that you wish to execute on the remote host
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e.g. "select * from pg_class"
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Outputs
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Returns setof int (pointer)
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Example usage
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select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd','select f1, f2 from mytable');
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==================================================================
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Name
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dblink_tok -- Returns individual select field results from a dblink remote query
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Synopsis
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dblink_tok(int pointer, int fnumber)
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Inputs
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pointer
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a pointer returned by a call to dblink()
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fnumber
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the ordinal position (zero based) of the field to be returned from the dblink result set
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Outputs
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Returns text
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Example usage
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select dblink_tok(t1.dblink_p,0) as f1, dblink_tok(t1.dblink_p,1) as f2
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from (select dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
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,'select f1, f2 from mytable') as dblink_p) as t1;
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==================================================================
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NOTE: If you need to provide selection criteria in a WHERE clause, it is necessary
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to 'fake' a UNION, e.g.
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select
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dblink_tok(t1.dblink_p,0) as f1
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,dblink_tok(t1.dblink_p,1) as f2
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from
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(
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select dblink(
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'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
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,'select f1, f2 from mytable'
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) as dblink_p
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union
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select null,null where false
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) as t1
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where
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f1 = 'mycriteria';
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in order to work around an issue with the query optimizer. A more convenient way to approach
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this problem is to create a view:
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create view myremotetable as
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select
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dblink_tok(t1.dblink_p,0) as f1
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,dblink_tok(t1.dblink_p,1) as f2
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from
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(
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select dblink(
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'hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
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,'select f1, f2 from mytable'
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) as dblink_p
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union
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select null,null where false
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) as t1;
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Then you can simply write:
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select f1,f2 from myremotetable where f1 = 'mycriteria';
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==================================================================
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-- Joe Conway
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