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diff --git a/doc/src/sgml/html/contrib-dblink-function.html b/doc/src/sgml/html/contrib-dblink-function.html new file mode 100644 index 0000000..483bfdc --- /dev/null +++ b/doc/src/sgml/html/contrib-dblink-function.html @@ -0,0 +1,143 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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 Vsnapshot" /><link rel="prev" href="contrib-dblink-disconnect.html" title="dblink_disconnect" /><link rel="next" href="contrib-dblink-exec.html" title="dblink_exec" /></head><body id="docContent" class="container-fluid col-10"><div 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.12. dblink">Up</a></td><th width="60%" align="center">F.12. dblink</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 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 /></div><div class="refentry" id="CONTRIB-DBLINK-FUNCTION"><div class="titlepage"></div><a id="id-1.11.7.21.8.1" 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-1.11.7.21.8.5"><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-1.11.7.21.8.6"><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-1.11.7.21.8.7"><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-1.11.7.21.8.8"><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-1.11.7.21.8.9"><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" title="dblink_disconnect">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="dblink.html" title="F.12. dblink">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="contrib-dblink-exec.html" title="dblink_exec">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" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> dblink_exec</td></tr></table></div></body></html>
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