Provided by: postgres-xc-doc_1.1-2ubuntu2_all 
NAME
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
Note
The following description applies only to Postgres-XC
dblink module has not been tested with Postges-XC yet. Although there're no reason that dblink does not
run in Postgres-XC, the development team leaves the test and the use of this module entirely to users.
This section is identical to the corresponding PostgreSQL reference manual.
Note
The following description applies only to PostgreSQL
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
Note
The following description applies only to Postgres-XC
dblink module has not been tested with Postges-XC yet. Although there're no reason that dblink does not
run in Postgres-XC, the development team leaves the test and the use of this module entirely to users.
This section is identical to the corresponding PostgreSQL reference manual.
Note
The following description applies only to PostgreSQL
conname
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
Note
The following description applies only to Postgres-XC
dblink module has not been tested with Postges-XC yet. Although there're no reason that dblink does not
run in Postgres-XC, the development team leaves the test and the use of this module entirely to users.
This section is identical to the corresponding PostgreSQL reference manual.
Note
The following description applies only to PostgreSQL
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 queryotherwise PostgreSQL would not know what to
expect. Here is an example:
SELECT *
FROM dblink('dbname=mydb', '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 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 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
Note
The following description applies only to Postgres-XC
dblink module has not been tested with Postges-XC yet. Although there're no reason that dblink does not
run in Postgres-XC, the development team leaves the test and the use of this module entirely to users.
This section is identical to the corresponding PostgreSQL reference manual.
Note
The following description applies only to PostgreSQL
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', 'select proname, prosrc from pg_proc')
AS t1(proname name, prosrc text);
SELECT * FROM myremote_pg_proc WHERE proname LIKE 'bytea%';
EXAMPLES
Note
The following description applies only to Postgres-XC
dblink module has not been tested with Postges-XC yet. Although there're no reason that dblink does not
run in Postgres-XC, the development team leaves the test and the use of this module entirely to users.
This section is identical to the corresponding PostgreSQL reference manual.
Note
The following description applies only to PostgreSQL
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)
Postgres-XC 1.1 2014-04-07 DBLINK(3)