Can anybody help me?

I use PHP-admin to make a MySQL script for the following:

- I want to split a datefield into separate fields (Year, Month, Day) in the same table.
- and what about the other way around?

My structure is:

datum, date, 0000-00-00 -> must be split up in:
yid, int(4) -> Year
mid, int(2) -> Month
did, int(2) -> Day

in the same table.

I will be very pleased if somebody could help me sort this out.

Best regards!