NAME

       dblink - executes a query in a remote database

SYNOPSIS

       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

DESCRIPTION

       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.

ARGUMENTS

       connname
           Name of the connection to use; omit this parameter to use the unnamed connection.

       connstr
           A connection info string, as previously described for dblink_connect.

       sql
           The SQL query that you wish to execute in the remote database, for example select *
           from foo.

       fail_on_error
           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.

RETURN VALUE

       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 options=-csearch_path=',
                           '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.

NOTES

       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 options=-csearch_path=',
                           'select proname, prosrc from pg_proc')
               AS t1(proname name, prosrc text);

           SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';

EXAMPLES

           SELECT * FROM dblink('dbname=postgres options=-csearch_path=',
                                '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 options=-csearch_path=');
            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 options=-csearch_path=');
            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)