416 lines
11 KiB
Plaintext
416 lines
11 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 <mail@joeconway.com>, 2001, 2002,
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* ALL RIGHTS RESERVED;
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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 0.4 (7 April, 2002):
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Functions allowing remote database INSERT/UPDATE/DELETE/SELECT, and
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various utility functions.
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Tested under Linux (Red Hat 7.2) and PostgreSQL 7.2 and 7.3devel
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Release Notes:
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Version 0.4
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- removed cursor wrap around input sql to allow for remote
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execution of INSERT/UPDATE/DELETE
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- dblink now returns a resource id instead of a real pointer
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- added several utility functions -- see below
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Version 0.3
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- fixed dblink invalid pointer causing corrupt elog message
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- fixed dblink_tok improper handling of null results
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- fixed examples in README.dblink
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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(text,text) RETURNS setof int
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- returns a resource id for results from remote query
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dblink_tok(int,int) RETURNS text
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- extracts and returns individual field results
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dblink_strtok(text,text,int) RETURNS text
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- extracts and returns individual token from delimited text
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dblink_get_pkey(text) RETURNS setof text
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- returns the field names of a relation's primary key fields
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dblink_last_oid(int) RETURNS oid
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- returns the last inserted oid
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dblink_build_sql_insert(text,int2vector,int2,_text,_text) RETURNS text
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- builds an insert statement using a local tuple, replacing the
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selection key field values with alternate supplied values
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dblink_build_sql_delete(text,int2vector,int2,_text) RETURNS text
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- builds a delete statement using supplied values for selection
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key field values
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dblink_build_sql_update(text,int2vector,int2,_text,_text) RETURNS text
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- builds an update statement using a local tuple, replacing the
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selection key field values with alternate supplied values
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dblink_current_query() RETURNS text
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- returns the current query string
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dblink_replace(text,text,text) RETURNS text
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- replace all occurences of substring-a in the input-string
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with substring-b
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Documentation
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==================================================================
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Name
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dblink -- Returns a resource id for 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 (res_id)
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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'
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,'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 res_id, int fnumber)
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Inputs
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res_id
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a resource id 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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A more convenient way to use dblink may be to create a view:
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create view myremotetable as
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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=template1 user=postgres password=postgres'
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,'select proname, prosrc from pg_proc') as dblink_p) as t1;
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Then you can simply write:
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select f1, f2 from myremotetable where f1 like 'bytea%';
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==================================================================
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Name
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dblink_strtok -- Extracts and returns individual token from delimited text
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Synopsis
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dblink_strtok(text inputstring, text delimiter, int posn) RETURNS text
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Inputs
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inputstring
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any string you want to parse a token out of;
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e.g. 'f=1&g=3&h=4'
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delimiter
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a single character to use as the delimiter;
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e.g. '&' or '='
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posn
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the position of the token of interest, 0 based;
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e.g. 1
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Outputs
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Returns text
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Example usage
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test=# select dblink_strtok(dblink_strtok('f=1&g=3&h=4','&',1),'=',1);
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dblink_strtok
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---------------
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3
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(1 row)
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==================================================================
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Name
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dblink_get_pkey -- returns the field names of a relation's primary
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key fields
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Synopsis
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dblink_get_pkey(text relname) RETURNS setof text
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Inputs
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relname
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any relation name;
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e.g. 'foobar'
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Outputs
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Returns setof text -- one row for each primary key field, in order of
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precedence
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Example usage
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test=# select dblink_get_pkey('foobar');
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dblink_get_pkey
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-----------------
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f1
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f2
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f3
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f4
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f5
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(5 rows)
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==================================================================
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Name
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dblink_last_oid -- Returns last inserted oid
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Synopsis
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dblink_last_oid(int res_id) RETURNS oid
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Inputs
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res_id
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any resource id returned by dblink function;
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Outputs
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Returns oid of last inserted tuple
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Example usage
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test=# select dblink_last_oid(dblink('hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd'
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,'insert into mytable (f1, f2) values (1,2)'));
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dblink_last_oid
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----------------
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16553
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(1 row)
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==================================================================
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Name
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dblink_build_sql_insert -- builds an insert statement using a local
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tuple, replacing the selection key field
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values with alternate supplied values
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dblink_build_sql_delete -- builds a delete statement using supplied
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values for selection key field values
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dblink_build_sql_update -- builds an update statement using a local
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tuple, replacing the selection key field
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values with alternate supplied values
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Synopsis
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dblink_build_sql_insert(text relname
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,int2vector primary_key_attnums
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,int2 num_primary_key_atts
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,_text src_pk_att_vals_array
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,_text tgt_pk_att_vals_array) RETURNS text
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dblink_build_sql_delete(text relname
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,int2vector primary_key_attnums
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,int2 num_primary_key_atts
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,_text tgt_pk_att_vals_array) RETURNS text
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dblink_build_sql_update(text relname
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,int2vector primary_key_attnums
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,int2 num_primary_key_atts
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,_text src_pk_att_vals_array
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,_text tgt_pk_att_vals_array) RETURNS text
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Inputs
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relname
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any relation name;
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e.g. 'foobar'
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primary_key_attnums
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vector of primary key attnums (1 based, see pg_index.indkey);
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e.g. '1 2'
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num_primary_key_atts
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number of primary key attnums in the vector; e.g. 2
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src_pk_att_vals_array
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array of primary key values, used to look up the local matching
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tuple, the values of which are then used to construct the SQL
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statement
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tgt_pk_att_vals_array
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array of primary key values, used to replace the local tuple
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values in the SQL statement
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Outputs
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Returns text -- requested SQL statement
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Example usage
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test=# select dblink_build_sql_insert('foo','1 2',2,'{"1", "a"}','{"1", "b''a"}');
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dblink_build_sql_insert
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--------------------------------------------------
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INSERT INTO foo(f1,f2,f3) VALUES('1','b''a','1')
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(1 row)
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test=# select dblink_build_sql_delete('MyFoo','1 2',2,'{"1", "b"}');
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dblink_build_sql_delete
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---------------------------------------------
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DELETE FROM "MyFoo" WHERE f1='1' AND f2='b'
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(1 row)
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test=# select dblink_build_sql_update('foo','1 2',2,'{"1", "a"}','{"1", "b"}');
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dblink_build_sql_update
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-------------------------------------------------------------
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UPDATE foo SET f1='1',f2='b',f3='1' WHERE f1='1' AND f2='b'
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(1 row)
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==================================================================
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Name
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dblink_current_query -- returns the current query string
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Synopsis
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dblink_current_query () RETURNS text
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Inputs
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None
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Outputs
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Returns text -- a copy of the currently executing query
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Example usage
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test=# select dblink_current_query() from (select dblink('dbname=template1','select oid, proname from pg_proc where proname = ''byteacat''') as f1) as t1;
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dblink_current_query
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-----------------------------------------------------------------------------------------------------------------------------------------------------
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select dblink_current_query() from (select dblink('dbname=template1','select oid, proname from pg_proc where proname = ''byteacat''') as f1) as t1;
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(1 row)
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==================================================================
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Name
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dblink_replace -- replace all occurences of substring-a in the
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input-string with substring-b
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Synopsis
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dblink_replace(text input-string, text substring-a, text substring-b) RETURNS text
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Inputs
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input-string
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the starting string, before replacement of substring-a
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substring-a
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the substring to find and replace
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substring-b
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the substring to be substituted in place of substring-a
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Outputs
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Returns text -- a copy of the starting string, but with all occurences of
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substring-a replaced with substring-b
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Example usage
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test=# select dblink_replace('12345678901234567890','56','hello');
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dblink_replace
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----------------------------
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1234hello78901234hello7890
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(1 row)
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==================================================================
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-- Joe Conway
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