which takes more space in a database a datetime or separate date and time columns?
/* If you have need of both a date and time, it is usually better to use a
datetime datatype. It makes most queries slightly easier by not having
to combine data from different columns to get a particular moment.
It visually takes up less space in a DB, and it is also more common
practice, so has wider support.
Exceptions include when legacy support is needed for separate fields. */