/*
 * 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(name) 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(name,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(name,int2vector,int2,_text) RETURNS text
       - builds a delete statement using supplied values for selection
         key field values
     dblink_build_sql_update(name,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(name 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(name 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(name relname
                         ,int2vector primary_key_attnums
                         ,int2 num_primary_key_atts
                         ,_text tgt_pk_att_vals_array) RETURNS text
dblink_build_sql_update(name 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

