SELECT 
    CASE 
        WHEN latest_a > latest_b THEN 'Result A'
        ELSE 'Result B'
    END AS result
FROM (
    SELECT 
        COALESCE(MAX(timestamp_column), '1900-01-01') AS latest_a
    FROM 
        table_a
) AS a
CROSS JOIN (
    SELECT 
        COALESCE(MAX(timestamp_column), '1900-01-01') AS latest_b
    FROM 
        table_b
) AS b;