PostgreSQL 9.1.2 Documentation
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# dblink_connect

## Name

dblink_connect -- opens a persistent connection to a remote database

## Synopsis

    dblink_connect(text connstr) returns text
    dblink_connect(text connname, text connstr) returns text

## Description

`dblink_connect()` establishes a connection to a remote PostgreSQL database. The server and database to be contacted are identified through a standard libpq connection string. Optionally, a name can be assigned to the connection. Multiple named connections can be open at once, but only one unnamed connection is permitted at a time. The connection will persist until closed or until the database session is ended.

The connection string may also be the name of an existing foreign server. It is recommended to use the `postgresql_fdw_validator` when defining the corresponding foreign-data wrapper. See the example below, as well as the following: CREATE FOREIGN DATA WRAPPER, CREATE SERVER, CREATE USER MAPPING

## Arguments

`conname`

  The name to use for this connection; if omitted, an unnamed connection is opened, replacing any existing unnamed connection.

`connstr`

  libpq-style connection info string, for example `hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres password=mypasswd`. For details see `PQconnectdb` in Section 31.1.

## Return Value

Returns status, which is always `OK` (since any error causes the function to throw an error instead of returning).

## Notes

Only superusers may use `dblink_connect` to create non-password-authenticated connections. If non-superusers need this capability, use `dblink_connect_u` instead.

It is unwise to choose connection names that contain equal signs, as this opens a risk of confusion with connection info strings in other `dblink` functions.

## Examples

    SELECT dblink_connect('dbname=postgres');
     dblink_connect
    ----------------
     OK
    (1 row)

    SELECT dblink_connect('myconn', 'dbname=postgres');
     dblink_connect
    ----------------
     OK
    (1 row)

    -- FOREIGN DATA WRAPPER functionality
    -- Note: local connection must require password authentication for this to work properly
    --       Otherwise, you will receive the following error from dblink_connect():
    --       ----------------------------------------------------------------------
    --       ERROR:  password is required
    --       DETAIL:  Non-superuser cannot connect if the server does not request a password.
    --       HINT:  Target server's authentication method must be changed.
    CREATE USER dblink_regression_test WITH PASSWORD 'secret';
    CREATE FOREIGN DATA WRAPPER postgresql VALIDATOR postgresql_fdw_validator;
    CREATE SERVER fdtest FOREIGN DATA WRAPPER postgresql OPTIONS (hostaddr '127.0.0.1', dbname 'contrib_regression');

    CREATE USER MAPPING FOR dblink_regression_test SERVER fdtest OPTIONS (user 'dblink_regression_test', password 'secret');
    GRANT USAGE ON FOREIGN SERVER fdtest TO dblink_regression_test;
    GRANT SELECT ON TABLE foo TO dblink_regression_test;

    \set ORIGINAL_USER :USER
    \c - dblink_regression_test
    SELECT dblink_connect('myconn', 'fdtest');
     dblink_connect
    ----------------
     OK
    (1 row)

    SELECT * FROM dblink('myconn','SELECT * FROM foo') AS t(a int, b text, c text[]);
     a  | b |       c
    ----+---+---------------
      0 | a | {a0,b0,c0}
      1 | b | {a1,b1,c1}
      2 | c | {a2,b2,c2}
      3 | d | {a3,b3,c3}
      4 | e | {a4,b4,c4}
      5 | f | {a5,b5,c5}
      6 | g | {a6,b6,c6}
      7 | h | {a7,b7,c7}
      8 | i | {a8,b8,c8}
      9 | j | {a9,b9,c9}
     10 | k | {a10,b10,c10}
    (11 rows)

    \c - :ORIGINAL_USER
    REVOKE USAGE ON FOREIGN SERVER fdtest FROM dblink_regression_test;
    REVOKE SELECT ON TABLE foo FROM  dblink_regression_test;
    DROP USER MAPPING FOR dblink_regression_test SERVER fdtest;
    DROP USER dblink_regression_test;
    DROP SERVER fdtest;
    DROP FOREIGN DATA WRAPPER postgresql;

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