Thread: Creating database links

Linux platform using PostgreSQL v9.3

I've looked thru the documentation and I can't find where PostgreSQL allows for database links (something similar to
what'savailable in Oracle). 

Does anyone know how to accomplish this or point me in the right direction?

Thank you!
Denise

"Ferrell, Denise CTR NSWCDD, Z11" <denise.ferrell.ctr@navy.mil> writes:
> I've looked thru the documentation and I can't find where PostgreSQL allows for database links (something similar to
what'savailable in Oracle). 

Closest thing we've got is foreign tables based on the postgres_fdw
foreign data wrapper (or you could use a different wrapper if you
want to link to a non-Postgres database).

            regards, tom lane

Thank you.  This looks like it's what I'm looking for.

r,
Denise

-----Original Message-----
From: pgsql-admin-owner@postgresql.org [mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Jorge Fernandez
Sent: Thursday, May 22, 2014 11:22 AM
To: Tom Lane
Cc: Ferrell, Denise CTR NSWCDD, Z11; pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Creating database links

This is what we're using , don't forget to install db_link module

select * from dblink('host=1192.168.1.1 dbname=mydb port=5432 user=myuser password=my_password', 'select name from
country')as t1 (proname name, prosrc text); 


Best Regards...


2014-05-22 12:10 GMT-03:00 Tom Lane <tgl@sss.pgh.pa.us>:


    "Ferrell, Denise CTR NSWCDD, Z11" <denise.ferrell.ctr@navy.mil> writes:
    > I've looked thru the documentation and I can't find where PostgreSQL allows for database links (something similar
towhat's available in Oracle). 


    Closest thing we've got is foreign tables based on the postgres_fdw
    foreign data wrapper (or you could use a different wrapper if you
    want to link to a non-Postgres database).

                            regards, tom lane


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--

Jorge Daniel Fernandez

Leader - DBA Team


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w: www.openenglish.com <http://www.openenglish.com/>


 <http://www.openenglish.com/>
Opensoft Argentina S.R.L
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Hi Jorge,

What would be the syntax for extracting all columns from a database table using dblink?  Could this be used if you are
unsureof the structure of the table you're extracting from? 

Thank you in advance,
d


    -----Original Message-----
    From: pgsql-admin-owner@postgresql.org [mailto:pgsql-admin-owner@postgresql.org] On Behalf Of Jorge Fernandez
    Sent: Thursday, May 22, 2014 11:22 AM
    To: Tom Lane
    Cc: Ferrell, Denise CTR NSWCDD, Z11; pgsql-admin@postgresql.org
    Subject: Re: [ADMIN] Creating database links


    This is what we're using , don't forget to install db_link module

    select * from dblink('host=1192.168.1.1 dbname=mydb port=5432 user=myuser password=my_password', 'select name from
country')as t1 (proname name, prosrc text); 


    Best Regards...


    2014-05-22 12:10 GMT-03:00 Tom Lane <tgl@sss.pgh.pa.us>:


            "Ferrell, Denise CTR NSWCDD, Z11" <denise.ferrell.ctr@navy.mil> writes:
            > I've looked thru the documentation and I can't find where PostgreSQL allows for database links (something
similarto what's available in Oracle). 


            Closest thing we've got is foreign tables based on the postgres_fdw
            foreign data wrapper (or you could use a different wrapper if you
            want to link to a non-Postgres database).

                                    regards, tom lane


            --
            Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org)
            To make changes to your subscription:
            http://www.postgresql.org/mailpref/pgsql-admin





    --

    Jorge Daniel Fernandez

    Leader - DBA Team


    S: elgaita99   |  t:@openenglish

    w: www.openenglish.com <http://www.openenglish.com/>


     <http://www.openenglish.com/>

    Opensoft Argentina S.R.L
    552 Suipacha , Piso 3to, Capital Federal Argentina, (C1022AAR)


    (*) The content of this electronic message may be privileged and confidential.
    (*) If you are not an intended recipient of this email, please delete it and do not use it.
    (*) The Open English name and the Open English logo are registered trademarks.
    (*) Opensoft Argentina S.R.L is a vendor company of Open English LLC.




    <http://www.openenglish.com/>





--

Jorge Daniel Fernandez

Leader - DBA Team


S: elgaita99   |  t:@openenglish
w: www.openenglish.com <http://www.openenglish.com/>


 <http://www.openenglish.com/>
Opensoft Argentina S.R.L
552 Suipacha , Piso 3to, Capital Federal Argentina, (C1022AAR)


(*) The content of this electronic message may be privileged and confidential.
(*) If you are not an intended recipient of this email, please delete it and do not use it.
(*) The Open English name and the Open English logo are registered trademarks.
(*) Opensoft Argentina S.R.L is a vendor company of Open English LLC.



<http://www.openenglish.com/>

Denise,

* Ferrell, Denise CTR NSWCDD, Z11 (denise.ferrell.ctr@navy.mil) wrote:
> What would be the syntax for extracting all columns from a database table using dblink?  Could this be used if you
areunsure of the structure of the table you're extracting from? 

To grab all columns from a remote table, you could use:

select row_to_json(apples) from apples;

This would return a json blob, but unfortunately you can't trivially
convert that into a record at this time.  You could turn it into a set
of key/value pairs though:

select
  b.*
from (select row_to_json(data.*) from data) as a,
     lateral json_each(a.row_to_json) as b;

You could write a PL/pgsql procedure to query the remote catalog and
determine what the columns are and create the view using dblink
accordingly too.

To get the columns for a database table, you can query pg_attribute,
with pg_class, like so:

-- Get the column names for the 'apples' table
-- attnum > 0 avoids internal PG columns
select
  attname
from
  pg_attribute
  join pg_class on (attrelid = oid)
where relname = 'apples'
  and attnum > 0;

You would need to include pg_namespace if you might have an 'apples'
table in multiple schemas.

What would probably be interesting to you also is the new IMPORT FOREIGN
SCHEMA capability which was recently added to PG and will be in
PostgreSQL 9.5:

http://www.postgresql.org/docs/devel/static/sql-importforeignschema.html

Or, perhaps, just using the postgres_fdw and foreign data tables instead
of using dblink at all might work.

    Thanks!

        Stephen