select
some_table.a_column,
some_table.a_2ndcolumn
FROM
some_table 
UNION 
select
another_table.a_3rdcolumn,
another_table.a_4thcolumn
FROM another_table
WHERE
some_table.a_date_column <=  to_date('20071111', 'YYYYMMDD') AND
some_table.a2nd_date_column  >=  to_date('20071111', 'YYYYMMDD')
}