Re: cross database queries?

On 2013.06.26 12:47 PM, John R Pierce wrote:
> On 6/26/2013 12:29 PM, Andrew Snyder wrote:
>> Thank you all for your replies.  I am indeed talking about working with
>> multiple back ends (oracle, mysql, or any valid DBI module) in the same query.
>
> thats never going to happen.   DBI is not a sql processor, its just an
> interface, the SQL is passed directly to the database server you're connected to

Never say never!  I'm working on a Perl-native engine right now, and it will not 
only be functionally complete internally but also has the option to federate to 
multiple back-ends, so then you can do what you want.

> some databases have support for 'foreign data wrappers', where you can
> explicitly setup a connection to another database then use tables on that
> foreign database, so if you connected to a DB like this and got the FDW stuff
> all working, you could maybe achieve what you want, but its almost never optimal
> as the planner for the 'primary' database has no way to optimize JOIN operations
> etc involving other databases.

In the short term that might be a good bet though, try using an existing SQL 
database's FDW capabilities.

-- Darren Duncan