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README.dblink |
/* * 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