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'\" t
.\" Title: dblink
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\" Date: 2024
.\" Manual: PostgreSQL 16.3 Documentation
.\" Source: PostgreSQL 16.3
.\" Language: English
.\"
.TH "DBLINK" "3" "2024" "PostgreSQL 16.3" "PostgreSQL 16.3 Documentation"
.\" -----------------------------------------------------------------
.\" * Define some portability stuff
.\" -----------------------------------------------------------------
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.\" http://bugs.debian.org/507673
.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\" -----------------------------------------------------------------
.\" * set default formatting
.\" -----------------------------------------------------------------
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.\" -----------------------------------------------------------------
.\" * MAIN CONTENT STARTS HERE *
.\" -----------------------------------------------------------------
.SH "NAME"
dblink \- executes a query in a remote database
.SH "SYNOPSIS"
.sp
.nf
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
.fi
.SH "DESCRIPTION"
.PP
\fBdblink\fR
executes a query (usually a
\fBSELECT\fR, but it can be any SQL statement that returns rows) in a remote database\&.
.PP
When two
text
arguments are given, the first one is first looked up as a persistent connection\*(Aqs 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
\fBdblink_connect\fR, and the indicated connection is made just for the duration of this command\&.
.SH "ARGUMENTS"
.PP
\fIconnname\fR
.RS 4
Name of the connection to use; omit this parameter to use the unnamed connection\&.
.RE
.PP
\fIconnstr\fR
.RS 4
A connection info string, as previously described for
\fBdblink_connect\fR\&.
.RE
.PP
\fIsql\fR
.RS 4
The SQL query that you wish to execute in the remote database, for example
select * from foo\&.
.RE
.PP
\fIfail_on_error\fR
.RS 4
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\&.
.RE
.SH "RETURN VALUE"
.PP
The function returns the row(s) produced by the query\&. Since
\fBdblink\fR
can be used with any query, it is declared to return
record, rather than specifying any particular set of columns\&. This means that you must specify the expected set of columns in the calling query \(em otherwise
PostgreSQL
would not know what to expect\&. Here is an example:
.sp
.if n \{\
.RS 4
.\}
.nf
SELECT *
FROM dblink(\*(Aqdbname=mydb options=\-csearch_path=\*(Aq,
\*(Aqselect proname, prosrc from pg_proc\*(Aq)
AS t1(proname name, prosrc text)
WHERE proname LIKE \*(Aqbytea%\*(Aq;
.fi
.if n \{\
.RE
.\}
.sp
The
\(lqalias\(rq
part of the
FROM
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
PostgreSQL
extension\&.) This allows the system to understand what
*
should expand to, and what
proname
in the
WHERE
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
FROM
clause\&. The column names need not match, however, and
\fBdblink\fR
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
FROM
clause\&.
.SH "NOTES"
.PP
A convenient way to use
\fBdblink\fR
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,
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE VIEW myremote_pg_proc AS
SELECT *
FROM dblink(\*(Aqdbname=postgres options=\-csearch_path=\*(Aq,
\*(Aqselect proname, prosrc from pg_proc\*(Aq)
AS t1(proname name, prosrc text);
SELECT * FROM myremote_pg_proc WHERE proname LIKE \*(Aqbytea%\*(Aq;
.fi
.if n \{\
.RE
.\}
.SH "EXAMPLES"
.sp
.if n \{\
.RS 4
.\}
.nf
SELECT * FROM dblink(\*(Aqdbname=postgres options=\-csearch_path=\*(Aq,
\*(Aqselect proname, prosrc from pg_proc\*(Aq)
AS t1(proname name, prosrc text) WHERE proname LIKE \*(Aqbytea%\*(Aq;
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(\*(Aqdbname=postgres options=\-csearch_path=\*(Aq);
dblink_connect
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
OK
(1 row)
SELECT * FROM dblink(\*(Aqselect proname, prosrc from pg_proc\*(Aq)
AS t1(proname name, prosrc text) WHERE proname LIKE \*(Aqbytea%\*(Aq;
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(\*(Aqmyconn\*(Aq, \*(Aqdbname=regression options=\-csearch_path=\*(Aq);
dblink_connect
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
OK
(1 row)
SELECT * FROM dblink(\*(Aqmyconn\*(Aq, \*(Aqselect proname, prosrc from pg_proc\*(Aq)
AS t1(proname name, prosrc text) WHERE proname LIKE \*(Aqbytea%\*(Aq;
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)
.fi
.if n \{\
.RE
.\}
|
