使用条件大小写在两个时间戳之间进行选择

I have a table and want to get records where now (current timestamp) between two timestamps (if not null):

id title start      end
1  A     1450718820 1450719000  
2  B     null       null
3  C     1450718820 null
4  D     null       1450718000  

Example 1: if current timestamp - 1450717990 I need records with ID: 2,4
Example 2: if current timestamp - 1450718830 I need records with ID: 1,2,3
Example 3: if current timestamp - 1450719010 I need records with ID: 2,3

Thanks! start and end are bigint(20) fields

You can use logic such as:

select t.*
from t
where (start is null or unix_timestamp() >= start) and
      (end is null or unix_timestamp() <= end);