CASE SELECT syntax

What about a SELECT syntax like that?

SELECT
CASE WHEN bar.foo_id IS NULL THEN bar.*
ELSE foo.*
FROM foo, bar

Anyway, I need a SELECT query that gets data from a FIRST TABLE if a
specific value in a SECOND TABLE is NULL or from SECOND TABLE itself if
the value IS NOT NULL.

Any suggestion?

Thank you!
--
Marco Lazzeri [ n o z e S.r.l. ]
Via Giuntini, 25/29 - 56023 Navacchio - Cascina (PI)
Tel +39 (0)50 754380 - Fax +39 (0)50 754381
mailto:marcomail(at)noze(dot)it - http://www.noze.it