/*
* dblink
*
* Functions returning results from a remote database
*
* Copyright (c) Joseph Conway <mail@joeconway.com>, 2001, 2002,
* ALL RIGHTS RESERVED;
*
* 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 0.4 (7 April, 2002):
Functions allowing remote database INSERT/UPDATE/DELETE/SELECT, and
various utility functions.
Tested under Linux (Red Hat 7.2) and PostgreSQL 7.2 and 7.3devel
Release Notes:
Version 0.4
- removed cursor wrap around input sql to allow for remote
execution of INSERT/UPDATE/DELETE
- dblink now returns a resource id instead of a real pointer
- added several utility functions -- see below
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(text,text) RETURNS setof int
- returns a resource id for results from remote query
dblink_tok(int,int) RETURNS text
- extracts and returns individual field results
dblink_strtok(text,text,int) RETURNS text
- extracts and returns individual token from delimited text
dblink_get_pkey(text) RETURNS setof text
- returns the field names of a relation's primary key fields
dblink_last_oid(int) RETURNS oid
- returns the last inserted oid
dblink_build_sql_insert(text,int2vector,int2,_text,_text) RETURNS text
- builds an insert statement using a local tuple, replacing the
selection key field values with alternate supplied values
dblink_build_sql_delete(text,int2vector,int2,_text) RETURNS text
- builds a delete statement using supplied values for selection
key field values
dblink_build_sql_update(text,int2vector,int2,_text,_text) RETURNS text
- builds an update statement using a local tuple, replacing the
selection key field values with alternate supplied values
dblink_current_query() RETURNS text
- returns the current query string
dblink_replace(text,text,text) RETURNS text
- replace all occurences of substring-a in the input-string
with substring-b
Documentation
==================================================================
Name
dblink -- Returns a resource id for 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 (res_id)
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 res_id, int fnumber)
Inputs
res_id
a resource id 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;
==================================================================
A more convenient way to use dblink may be 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=template1 user=postgres password=postgres'
,'select proname, prosrc from pg_proc') as dblink_p) as t1;
Then you can simply write:
select f1, f2 from myremotetable where f1 like 'bytea%';
==================================================================
Name
dblink_strtok -- Extracts and returns individual token from delimited text
Synopsis
dblink_strtok(text inputstring, text delimiter, int posn) RETURNS text
Inputs
inputstring
any string you want to parse a token out of;
e.g. 'f=1&g=3&h=4'
delimiter
a single character to use as the delimiter;
e.g. '&' or '='
posn
the position of the token of interest, 0 based;
e.g. 1
Outputs
Returns text
Example usage
test=# select dblink_strtok(dblink_strtok('f=1&g=3&h=4','&',1),'=',1);
dblink_strtok
---------------
3
(1 row)
==================================================================
Name
dblink_get_pkey -- returns the field names of a relation's primary
key fields
Synopsis
dblink_get_pkey(text relname) RETURNS setof text
Inputs
relname
any relation name;
e.g. 'foobar'
Outputs
Returns setof text -- one row for each primary key field, in order of
precedence
Example usage
test=# select dblink_get_pkey('foobar');
dblink_get_pkey
-----------------
f1
f2
f3
f4
f5
(5 rows)
==================================================================
Name
dblink_last_oid -- Returns last inserted oid
Synopsis
dblink_last_oid(int res_id) RETURNS oid
Inputs
res_id
any resource id returned by dblink function;
Outputs
Returns oid of last inserted tuple
Example usage
test=# select dblink_last_oid(dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
,'insert into mytable (f1, f2) values (1,2)'));
dblink_last_oid
----------------
16553
(1 row)
==================================================================
Name
dblink_build_sql_insert -- builds an insert statement using a local
tuple, replacing the selection key field
values with alternate supplied values
dblink_build_sql_delete -- builds a delete statement using supplied
values for selection key field values
dblink_build_sql_update -- builds an update statement using a local
tuple, replacing the selection key field
values with alternate supplied values
Synopsis
dblink_build_sql_insert(text relname
,int2vector primary_key_attnums
,int2 num_primary_key_atts
,_text src_pk_att_vals_array
,_text tgt_pk_att_vals_array) RETURNS text
dblink_build_sql_delete(text relname
,int2vector primary_key_attnums
,int2 num_primary_key_atts
,_text tgt_pk_att_vals_array) RETURNS text
dblink_build_sql_update(text relname
,int2vector primary_key_attnums
,int2 num_primary_key_atts
,_text src_pk_att_vals_array
,_text tgt_pk_att_vals_array) RETURNS text
Inputs
relname
any relation name;
e.g. 'foobar'
primary_key_attnums
vector of primary key attnums (1 based, see pg_index.indkey);
e.g. '1 2'
num_primary_key_atts
number of primary key attnums in the vector; e.g. 2
src_pk_att_vals_array
array of primary key values, used to look up the local matching
tuple, the values of which are then used to construct the SQL
statement
tgt_pk_att_vals_array
array of primary key values, used to replace the local tuple
values in the SQL statement
Outputs
Returns text -- requested SQL statement
Example usage
test=# select dblink_build_sql_insert('foo','1 2',2,'{"1", "a"}','{"1", "b''a"}');
dblink_build_sql_insert
--------------------------------------------------
INSERT INTO foo(f1,f2,f3) VALUES('1','b''a','1')
(1 row)
test=# select dblink_build_sql_delete('MyFoo','1 2',2,'{"1", "b"}');
dblink_build_sql_delete
---------------------------------------------
DELETE FROM "MyFoo" WHERE f1='1' AND f2='b'
(1 row)
test=# select dblink_build_sql_update('foo','1 2',2,'{"1", "a"}','{"1", "b"}');
dblink_build_sql_update
-------------------------------------------------------------
UPDATE foo SET f1='1',f2='b',f3='1' WHERE f1='1' AND f2='b'
(1 row)
==================================================================
Name
dblink_current_query -- returns the current query string
Synopsis
dblink_current_query () RETURNS text
Inputs
None
Outputs
Returns text -- a copy of the currently executing query
Example usage
test=# select dblink_current_query() from (select dblink('dbname=template1','select oid, proname from pg_proc where proname = ''byteacat''') as f1) as t1;
dblink_current_query
-----------------------------------------------------------------------------------------------------------------------------------------------------
select dblink_current_query() from (select dblink('dbname=template1','select oid, proname from pg_proc where proname = ''byteacat''') as f1) as t1;
(1 row)
==================================================================
Name
dblink_replace -- replace all occurences of substring-a in the
input-string with substring-b
Synopsis
dblink_replace(text input-string, text substring-a, text substring-b) RETURNS text
Inputs
input-string
the starting string, before replacement of substring-a
substring-a
the substring to find and replace
substring-b
the substring to be substituted in place of substring-a
Outputs
Returns text -- a copy of the starting string, but with all occurences of
substring-a replaced with substring-b
Example usage
test=# select dblink_replace('12345678901234567890','56','hello');
dblink_replace
----------------------------
1234hello78901234hello7890
(1 row)
==================================================================
-- Joe Conway
5cabcfccce