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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >dblink</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="dblink" HREF="dblink.html"><LINK REL="PREVIOUS" TITLE="dblink_disconnect" HREF="contrib-dblink-disconnect.html"><LINK REL="NEXT" TITLE="dblink_exec" HREF="contrib-dblink-exec.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="REFENTRY" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="dblink_disconnect" HREF="contrib-dblink-disconnect.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="dblink.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="dblink_exec" HREF="contrib-dblink-exec.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="CONTRIB-DBLINK-FUNCTION" ></A >dblink</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN147248" ></A ><H2 >Name</H2 >dblink -- executes a query in a remote database</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN147251" ></A ><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" ><A NAME="AEN147253" ></A ><H2 >Description</H2 ><P > <CODE CLASS="FUNCTION" >dblink</CODE > executes a query (usually a <TT CLASS="COMMAND" >SELECT</TT >, but it can be any SQL statement that returns rows) in a remote database. </P ><P > When two <TT CLASS="TYPE" >text</TT > 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" ><A NAME="AEN147261" ></A ><H2 >Arguments</H2 ><P ></P ><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="PARAMETER" >connname</TT ></DT ><DD ><P > Name of the connection to use; omit this parameter to use the unnamed connection. </P ></DD ><DT ><TT CLASS="PARAMETER" >connstr</TT ></DT ><DD ><P > A connection info string, as previously described for <CODE CLASS="FUNCTION" >dblink_connect</CODE >. </P ></DD ><DT ><TT CLASS="PARAMETER" >sql</TT ></DT ><DD ><P > The SQL query that you wish to execute in the remote database, for example <TT CLASS="LITERAL" >select * from foo</TT >. </P ></DD ><DT ><TT CLASS="PARAMETER" >fail_on_error</TT ></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" ><A NAME="AEN147286" ></A ><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 <TT CLASS="TYPE" >record</TT >, 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', 'select proname, prosrc from pg_proc') AS t1(proname name, prosrc text) WHERE proname LIKE 'bytea%';</PRE ><P> The <SPAN CLASS="QUOTE" >"alias"</SPAN > part of the <TT CLASS="LITERAL" >FROM</TT > 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 <TT CLASS="LITERAL" >*</TT > should expand to, and what <TT CLASS="STRUCTNAME" >proname</TT > in the <TT CLASS="LITERAL" >WHERE</TT > 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 <TT CLASS="LITERAL" >FROM</TT > 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 <TT CLASS="LITERAL" >FROM</TT > clause. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN147302" ></A ><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', 'select proname, prosrc from pg_proc') AS t1(proname name, prosrc text); SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';</PRE ><P></P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN147307" ></A ><H2 >Examples</H2 ><PRE CLASS="SCREEN" >SELECT * FROM dblink('dbname=postgres', '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'); 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'); 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 CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="contrib-dblink-disconnect.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="contrib-dblink-exec.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >dblink_disconnect</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="dblink.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >dblink_exec</TD ></TR ></TABLE ></DIV ></BODY ></HTML >