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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>dblink_connect</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="dblink.html" title="F.10. dblink" /><link rel="next" href="contrib-dblink-connect-u.html" title="dblink_connect_u" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">dblink_connect</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="dblink.html" title="F.10. dblink">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="dblink.html" title="F.10. dblink">Up</a></td><th width="60%" align="center">F.10. dblink</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="contrib-dblink-connect-u.html" title="dblink_connect_u">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="CONTRIB-DBLINK-CONNECT"><div class="titlepage"></div><a id="id-1.11.7.19.5.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">dblink_connect</span></h2><p>dblink_connect — opens a persistent connection to a remote database</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
dblink_connect(text connstr) returns text
dblink_connect(text connname, text connstr) returns text
</pre></div><div class="refsect1" id="id-1.11.7.19.5.5"><h2>Description</h2><p>
<code class="function">dblink_connect()</code> establishes a connection to a remote
<span class="productname">PostgreSQL</span> database. The server and database to
be contacted are identified through a standard <span class="application">libpq</span>
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.
</p><p>
The connection string may also be the name of an existing foreign
server. It is recommended to use the foreign-data wrapper
<code class="literal">dblink_fdw</code> when defining the foreign
server. See the example below, as well as
<a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a> and
<a class="xref" href="sql-createusermapping.html" title="CREATE USER MAPPING"><span class="refentrytitle">CREATE USER MAPPING</span></a>.
</p></div><div class="refsect1" id="id-1.11.7.19.5.6"><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>connname</code></em></span></dt><dd><p>
The name to use for this connection; if omitted, an unnamed
connection is opened, replacing any existing unnamed connection.
</p></dd><dt><span class="term"><em class="parameter"><code>connstr</code></em></span></dt><dd><p><span class="application">libpq</span>-style connection info string, for example
<code class="literal">hostaddr=127.0.0.1 port=5432 dbname=mydb user=postgres
password=mypasswd options=-csearch_path=</code>.
For details see <a class="xref" href="libpq-connect.html#LIBPQ-CONNSTRING" title="33.1.1. Connection Strings">Section 33.1.1</a>.
Alternatively, the name of a foreign server.
</p></dd></dl></div></div><div class="refsect1" id="id-1.11.7.19.5.7"><h2>Return Value</h2><p>
Returns status, which is always <code class="literal">OK</code> (since any error
causes the function to throw an error instead of returning).
</p></div><div class="refsect1" id="id-1.11.7.19.5.8"><h2>Notes</h2><p>
If untrusted users have access to a database that has not adopted a
<a class="link" href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS" title="5.9.6. Usage Patterns">secure schema usage pattern</a>,
begin each session by removing publicly-writable schemas from
<code class="varname">search_path</code>. One could, for example,
add <code class="literal">options=-csearch_path=</code> to
<em class="parameter"><code>connstr</code></em>. This consideration is not specific
to <code class="filename">dblink</code>; it applies to every interface for
executing arbitrary SQL commands.
</p><p>
Only superusers may use <code class="function">dblink_connect</code> to create
non-password-authenticated connections. If non-superusers need this
capability, use <code class="function">dblink_connect_u</code> instead.
</p><p>
It is unwise to choose connection names that contain equal signs,
as this opens a risk of confusion with connection info strings
in other <code class="filename">dblink</code> functions.
</p></div><div class="refsect1" id="id-1.11.7.19.5.9"><h2>Examples</h2><pre class="screen">
SELECT dblink_connect('dbname=postgres options=-csearch_path=');
dblink_connect
----------------
OK
(1 row)
SELECT dblink_connect('myconn', 'dbname=postgres options=-csearch_path=');
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 SERVER fdtest FOREIGN DATA WRAPPER dblink_fdw OPTIONS (hostaddr '127.0.0.1', dbname 'contrib_regression');
CREATE USER regress_dblink_user WITH PASSWORD 'secret';
CREATE USER MAPPING FOR regress_dblink_user SERVER fdtest OPTIONS (user 'regress_dblink_user', password 'secret');
GRANT USAGE ON FOREIGN SERVER fdtest TO regress_dblink_user;
GRANT SELECT ON TABLE foo TO regress_dblink_user;
\set ORIGINAL_USER :USER
\c - regress_dblink_user
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 regress_dblink_user;
REVOKE SELECT ON TABLE foo FROM regress_dblink_user;
DROP USER MAPPING FOR regress_dblink_user SERVER fdtest;
DROP USER regress_dblink_user;
DROP SERVER fdtest;
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