dblink(text connname, text sql [, bool fail_on_error]) returns setof record dblink(text connstr, text sql [, bool fail_on_error]) returns setof record dblink(text sql [, bool fail_on_error]) returns setof record
    dblink executes a query (usually a SELECT,
    but it can be any SQL statement that returns rows) in a remote database.
   
    When two text arguments are given, the first one is first
    looked up as a persistent connection's name; if found, the command
    is executed on that connection.  If not found, the first argument
    is treated as a connection info string as for dblink_connect,
    and the indicated connection is made just for the duration of this command.
   
Name of the connection to use; omit this parameter to use the unnamed connection.
       A connection info string, as previously described for
       dblink_connect.
      
The SQL query that you wish to execute in the remote database, for example select * from foo.
If true (the default when omitted) then an error thrown on the remote side of the connection causes an error to also be thrown locally. If false, the remote error is locally reported as a NOTICE, and the function returns no rows.
    The function returns the row(s) produced by the query.  Since
    dblink can be used with any query, it is declared
    to return record, rather than specifying any particular
    set of columns.  This means that you must specify the expected
    set of columns in the calling query — otherwise
    PostgreSQL would not know what to expect.
    Here is an example:
SELECT *
    FROM dblink('dbname=mydb', 'select proname, prosrc from pg_proc')
      AS t1(proname name, prosrc text)
    WHERE proname LIKE 'bytea%';
    The "alias" part of the FROM clause must
    specify the column names and types that the function will return.
    (Specifying column names in an alias is actually standard SQL
    syntax, but specifying column types is a PostgreSQL
    extension.)  This allows the system to understand what
    * should expand to, and what proname
    in the WHERE clause refers to, in advance of trying
    to execute the function.  At run time, an error will be thrown
    if the actual query result from the remote database does not
    have the same number of columns shown in the FROM clause.
    The column names need not match, however, and dblink
    does not insist on exact type matches either.  It will succeed
    so long as the returned data strings are valid input for the
    column type declared in the FROM clause.
   
    dblink fetches the entire remote query result before
    returning any of it to the local system.  If the query is expected
    to return a large number of rows, it's better to open it as a cursor
    with dblink_open and then fetch a manageable number
    of rows at a time.
   
    A convenient way to use dblink with predetermined
    queries is to create a view.
    This allows the column type information to be buried in the view,
    instead of having to spell it out in every query.  For example,
CREATE VIEW myremote_pg_proc AS
  SELECT *
    FROM dblink('dbname=postgres', 'select proname, prosrc from pg_proc')
    AS t1(proname name, prosrc text);
SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';SELECT * FROM dblink('dbname=postgres', 'select proname, prosrc from pg_proc')
  AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
  proname   |   prosrc
------------+------------
 byteacat   | byteacat
 byteaeq    | byteaeq
 bytealt    | bytealt
 byteale    | byteale
 byteagt    | byteagt
 byteage    | byteage
 byteane    | byteane
 byteacmp   | byteacmp
 bytealike  | bytealike
 byteanlike | byteanlike
 byteain    | byteain
 byteaout   | byteaout
(12 rows)
SELECT dblink_connect('dbname=postgres');
 dblink_connect
----------------
 OK
(1 row)
SELECT * FROM dblink('select proname, prosrc from pg_proc')
  AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
  proname   |   prosrc
------------+------------
 byteacat   | byteacat
 byteaeq    | byteaeq
 bytealt    | bytealt
 byteale    | byteale
 byteagt    | byteagt
 byteage    | byteage
 byteane    | byteane
 byteacmp   | byteacmp
 bytealike  | bytealike
 byteanlike | byteanlike
 byteain    | byteain
 byteaout   | byteaout
(12 rows)
SELECT dblink_connect('myconn', 'dbname=regression');
 dblink_connect
----------------
 OK
(1 row)
SELECT * FROM dblink('myconn', 'select proname, prosrc from pg_proc')
  AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';
  proname   |   prosrc
------------+------------
 bytearecv  | bytearecv
 byteasend  | byteasend
 byteale    | byteale
 byteagt    | byteagt
 byteage    | byteage
 byteane    | byteane
 byteacmp   | byteacmp
 bytealike  | bytealike
 byteanlike | byteanlike
 byteacat   | byteacat
 byteaeq    | byteaeq
 bytealt    | bytealt
 byteain    | byteain
 byteaout   | byteaout
(14 rows)