How to use (install) dblink in PostgreSQL?

问题

I am used to Oracle and to create a dblink in my schema and then access to a remote database like this: mytable@myremotedb, is there anyway do to the same with PostgreSQL?

Right now I am using dblink like this:

SELECT logindate FROM dblink('host=dev.toto.com
                              user=toto
                              password=isok
                              dbname=totofamily', 'SELECT logindate FROM loginlog');

When I execute this command I get the following error:

HINT: No function matches the given name and argument types. You might need to add explicit type casts.

Does anybody have an idea ? Do we have to "activate" dblinks or do something before using them?

Is there something to do on the remote database we are going to query? Do we have to activate dblink too? I keep having a could not establish connection. This is the line is type:

SELECT dblink_connect_u('host=x.x.x.x dbname=mydb user=root port=5432');

IP Address is correct and Postgres is running on the remote server. Any idea?

回答1:

With PostgreSQL 9.1 or later, installation of additional modules has been simplified. Registered extensions (including dblink) can be installed with CREATE EXTENSION:

CREATE EXTENSION dblink;

Installs into your default schema (public by default). Make sure your search_path is set properly before you run the command and the schema is visible to all users who have to work with it.

Alternatively, you can install to any schema of your choice with:

CREATE EXTENSION dblink SCHEMA extensions;

See:

Best way to install hstore on multiple schemas in a Postgres database?

Run once per database. Or run it in the standard system database template1 to add it to every newly created DB automatically. Details in the manual.

You need to have the files providing the module installed on the server first. For Debian and derivatives this would be the package postgresql-contrib-9.1 - for PostgreSQL 9.1, obviously.

回答2:

I am using DBLINK to connect internal database for cross database queries.

Reference taken from this article.

Install DbLink extension.

CREATE EXTENSION dblink;

Verify DbLink:

SELECT pg_namespace.nspname, pg_proc.proname 
FROM pg_proc, pg_namespace 
WHERE pg_proc.pronamespace=pg_namespace.oid 
   AND pg_proc.proname LIKE '%dblink%';

Test connection of database:

SELECT dblink_connect('host=localhost user=postgres password=enjoy dbname=postgres');

回答3:

On linux, find dblink.sql, then execute in the postgresql console something like this to create all required functions:

\i /usr/share/postgresql/8.4/contrib/dblink.sql

you might need to install the contrib packages: sudo apt-get install postgresql-contrib

回答4:

Installing modules usually requires you to run an sql script that is included with the database installation.

Assuming linux-like OS

find / -name dblink.sql

Verify the location and run it

回答5:

It can be added by using:

$psql -d databaseName -c "CREATE EXTENSION dblink"

回答6:

# or even faster copy paste answer if you have sudo on the host 
sudo su - postgres  -c "psql template1 -c 'CREATE EXTENSION IF NOT EXISTS \"dblink\";'"

来源：https://stackoverflow.com/questions/3862648/how-to-use-install-dblink-in-postgresql

标签

sql

postgresql

dblink