Services
  • 24×7×365 Technical Support
  • Migration to PostgreSQL
  • High Availability Deployment
  • Database Audit
  • Remote DBA for PostgreSQL
Products
  • Postgres Pro Enterprise
  • Postgres Pro Standard
  • Cloud Solutions
  • Postgres Extensions
Resources
  • Blog
  • Documentation
  • Webinars
  • Videos
  • Presentations
Community
  • Events
  • Training Courses
  • Books
  • Demo Database
  • Mailing List Archives
About
  • Leadership team
  • Partners
  • Customers
  • In the News
  • Press Releases
  • Press Info

Facebook
Postgres Pro
  • Services
    24×7×365 Technical Support Migration to PostgreSQL High Availability Deployment Database Audit Remote DBA for PostgreSQL
  • Products
    Postgres Pro Enterprise Postgres Pro Standard Cloud Solutions Postgres Extensions
  • Resources
    Blog Documentation Webinars Videos Presentations
  • Community
    Events Training Courses Books Demo Database Mailing List Archives
  • About
    Leadership team Partners Customers In the News Press Releases Press Info
Facebook
Downloads
dblink
Prev UpF.13. dblinkHome Next

dblink

dblink — executes a query in a remote database

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

Description

dblink executes a query (usually a SELECT, but it can be any SQL statement that returns rows) in a remote database.

When two text 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 dblink_connect, and the indicated connection is made just for the duration of this command.

Arguments

connname

Name of the connection to use; omit this parameter to use the unnamed connection.

connstr

A connection info string, as previously described for dblink_connect.

sql

The SQL query that you wish to execute in the remote database, for example select * from foo.

fail_on_error

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.

Return Value

The function returns the row(s) produced by the query. Since dblink 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 — otherwise Postgres Pro would not know what to expect. Here is an example:

SELECT *
    FROM dblink('dbname=mydb options=-csearch_path=',
                'select proname, prosrc from pg_proc')
      AS t1(proname name, prosrc text)
    WHERE proname LIKE 'bytea%';

The “alias” 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 Postgres Pro 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 dblink 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.

Notes

A convenient way to use dblink 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,

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%';

Examples

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)

Prev Home Next
dblink_disconnect Up dblink_exec
epub pdf

This page in other versions:

Postgres Pro Standard 17
Postgres Pro Standard 16
Postgres Pro Standard 15
Postgres Pro Standard 14
Postgres Pro Standard 13
Postgres Pro Standard 12
Postgres Pro Standard 11
Postgres Pro Standard 10
Postgres Pro Standard 9.6
Postgres Pro Standard 9.5
Postgres Pro Enterprise 17
Postgres Pro Enterprise 16
Postgres Pro Enterprise 15
Postgres Pro Enterprise 14
Postgres Pro Enterprise 13
Postgres Pro Enterprise 12
Postgres Pro Enterprise 11
Postgres Pro Enterprise 10
Postgres Pro Enterprise 9.6
PostgreSQL 17
PostgreSQL 16
PostgreSQL 15
PostgreSQL 14
PostgreSQL 13
PostgreSQL 12
PostgreSQL 11
PostgreSQL 10
PostgreSQL 9.6
PostgreSQL 9.5
PostgreSQL 9.4
Есть вопросы? Напишите нам!

Соглашаюсь с условиями обработки персональных данных



✖
×
Postgres Pro Standard 17 Postgres Pro Standard 16 Postgres Pro Standard 15 Postgres Pro Standard 14 Postgres Pro Standard 13 Postgres Pro Standard 12 Postgres Pro Standard 11 Postgres Pro Standard 10 Postgres Pro Standard 9.6 Postgres Pro Standard 9.5
Postgres Pro Enterprise 17 Postgres Pro Enterprise 16 Postgres Pro Enterprise 15 Postgres Pro Enterprise 14 Postgres Pro Enterprise 13 Postgres Pro Enterprise 12 Postgres Pro Enterprise 11 Postgres Pro Enterprise 10 Postgres Pro Enterprise 9.6
PostgreSQL 17 PostgreSQL 16 PostgreSQL 15 PostgreSQL 14 PostgreSQL 13 PostgreSQL 12 PostgreSQL 11 PostgreSQL 10 PostgreSQL 9.6 PostgreSQL 9.5 PostgreSQL 9.4
Go to Postgres Pro Enterprise 9.6
Services
  • 24×7×365 Technical Support
  • Migration to PostgreSQL
  • High Availability Deployment
  • Database Audit
  • Remote DBA for PostgreSQL
Products
  • Postgres Pro Enterprise
  • Postgres Pro Standard
  • Cloud Solutions
  • Postgres Extensions
Resources
  • Blog
  • Documentation
  • Webinars
  • Videos
  • Presentations
Community
  • Events
  • Training Courses
  • Books
  • Demo Database
  • Mailing List Archives
About
  • Leadership team
  • Partners
  • Customers
  • In the News
  • Press Releases
  • Press Info
Products
  • Postgres Pro Enterprise
  • Postgres Pro Standard
  • Cloud Solutions
  • Postgres Extensions
Resources
  • Blog
  • Documentation
  • Webinars
  • Videos
  • Presentations
Services
  • 24×7×365 Technical Support
  • Migration to Postgres
  • High Availability Deployment
  • Database Audit
  • Remote DBA for PostgreSQL
Community
  • Events
  • Training Courses
  • Intro Book
  • Demo Database
  • Mailing List Archives
About
  • Leadership team
  • Partners
  • Customers
  • In the News
  • Press Releases
  • Press Info
Contacts
  • Neptune House, Marina Bay, office 207, Gibraltar, GX11 1AA
  • info@postgrespro.com
  • Facebook
Get in touch!



© Postgres Professional Europe Limited, 2015 — 2025
EULA EULA for Cloud Environments Privacy Policy GDPR Compliance Commitment
© Postgres Professional Europe Limited, 2015 — 2025
EULA
EULA for Cloud Environments
Privacy Policy
GDPR Compliance Commitment
By continuing to browse this website, you agree to the use of cookies. Go to Privacy Policy.