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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</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="contrib-dblink-disconnect.html" title="dblink_disconnect" /><link rel="next" href="contrib-dblink-exec.html" title="dblink_exec" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">dblink</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="contrib-dblink-disconnect.html" title="dblink_disconnect">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 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="contrib-dblink-exec.html" title="dblink_exec">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="CONTRIB-DBLINK-FUNCTION"><div class="titlepage"></div><a id="id-1.11.7.19.8.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">dblink</span></h2><p>dblink — executes a query in a remote database</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="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
- </pre></div><div class="refsect1" id="id-1.11.7.19.8.5"><h2>Description</h2><p>
- <code class="function">dblink</code> executes a query (usually a <code class="command">SELECT</code>,
- but it can be any SQL statement that returns rows) in a remote database.
- </p><p>
- When two <code class="type">text</code> 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 <code class="function">dblink_connect</code>,
- and the indicated connection is made just for the duration of this command.
- </p></div><div class="refsect1" id="id-1.11.7.19.8.6"><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>connname</code></em></span></dt><dd><p>
- Name of the connection to use; omit this parameter to use the
- unnamed connection.
- </p></dd><dt><span class="term"><em class="parameter"><code>connstr</code></em></span></dt><dd><p>
- A connection info string, as previously described for
- <code class="function">dblink_connect</code>.
- </p></dd><dt><span class="term"><em class="parameter"><code>sql</code></em></span></dt><dd><p>
- The SQL query that you wish to execute in the remote database,
- for example <code class="literal">select * from foo</code>.
- </p></dd><dt><span class="term"><em class="parameter"><code>fail_on_error</code></em></span></dt><dd><p>
- 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.
- </p></dd></dl></div></div><div class="refsect1" id="id-1.11.7.19.8.7"><h2>Return Value</h2><p>
- The function returns the row(s) produced by the query. Since
- <code class="function">dblink</code> can be used with any query, it is declared
- to return <code class="type">record</code>, rather than specifying any particular
- set of columns. This means that you must specify the expected
- set of columns in the calling query — otherwise
- <span class="productname">PostgreSQL</span> would not know what to expect.
- Here is an example:
-
- </p><pre class="programlisting">
- SELECT *
- FROM dblink('dbname=mydb options=-csearch_path=',
- 'select proname, prosrc from pg_proc')
- AS t1(proname name, prosrc text)
- WHERE proname LIKE 'bytea%';
- </pre><p>
-
- The <span class="quote">“<span class="quote">alias</span>”</span> part of the <code class="literal">FROM</code> 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 <span class="productname">PostgreSQL</span>
- extension.) This allows the system to understand what
- <code class="literal">*</code> should expand to, and what <code class="structname">proname</code>
- in the <code class="literal">WHERE</code> 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 <code class="literal">FROM</code> clause.
- The column names need not match, however, and <code class="function">dblink</code>
- 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 <code class="literal">FROM</code> clause.
- </p></div><div class="refsect1" id="id-1.11.7.19.8.8"><h2>Notes</h2><p>
- A convenient way to use <code class="function">dblink</code> 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,
-
- </p><pre class="programlisting">
- 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%';
- </pre></div><div class="refsect1" id="id-1.11.7.19.8.9"><h2>Examples</h2><pre class="screen">
- 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)
- </pre></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="contrib-dblink-disconnect.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="dblink.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="contrib-dblink-exec.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">dblink_disconnect </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> dblink_exec</td></tr></table></div></body></html>
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