Select between two databases

Hi,

Does any one know how I may select between two databases running on same
machine or on different machines eg.

select colA1 from tableA1 where colA2 in (select colB1 from tableB1);

here tableA1 and tableB1 are in different databases. The two databases
might be under the same postmaster or on different machines under
different postmasters. How do I query both simultaneously? Is it possible?

Thanks,
Indraneel

/************************************************************************.
# Indraneel Majumdar                  ¡  E-mail: indraneel@123india.com  #
# Bioinformatics Unit (EMBNET node),  ¡  URL: http://scorpius.iwarp.com  #
# Centre for DNA Fingerprinting and Diagnostics,                         #
# Hyderabad, India - 500076                                              #
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