Possible to have multiple data sources within 1 SQL querey?

Question

Hi All,
Is it possible to join to a table in a different datasource within 1 SQL Querey?
Something like...
Connection 1
Select *
From Table
Join
Connection 2
On
Connection1.Table1.Field1 = Connection2.Table2.Field2  Thanks,
John

Answer 1

Johnbr (Oracle11G) wrote:
Is it possible to join to a table in a different datasource within 1 SQL Querey?Called distributed joins - joining a table from one database with that of another database. Also possible to do heterogeneously across different database products - e.g. joining an Oracle table with a SQL-Server table.
As already explained, some kind of communication interface is needed from the local database to the remote database, in order for the remote table to be read and joined to the local database. This interface is called a database link in Oracle.
The basic steps. First define the database link:
create database link <linkname>
  connect to <account>
  identified by <password>
  using <connection-string>Complete syntax details and examples are in the SQL Reference Guide (see http://tahiti.oracle.com)
After the database link has been identified, you should now be able to address remote tables as follows:
select * from <remote-table>@<link-name>A distributed join would look something like the following:
select
from <local-table> t1,
      <remote-table>@<link-name> t2
where t1.. = t2..However... this is almost always a BAD IDEA to do distributed joins. It seldom performs well. Performance is immediately constrained to the speed, bandwidth and latency of the network link between local and remote databases. It cannot scale with data volumes and increased frequency of use.
So if the remote table is not small, the network link not robust and reliable, and join not infrequent, it is bad idea to make use of distributed joins. In which case other alternative (and far superior) features need to be considered instead - like materialised views.