UNION! thanks everyone!
i'll take this stuff up on the pgsql-sql list in the future.
union does intra- and inter- table distinct, notice `red' and `two':
test=> select str from foo ;
str
-----
one
two
two
red
(4 rows)
test=> select str from bar ;
str
--------
red
orange
yellow
green
blue
indigo
violet
red
(8 rows)
test=> select str from foo union ( select str from bar ) ;
str
--------
blue
green
indigo
one
orange
red
two
violet
yellow
(9 rows)