I would save memories in my opinion thats the most important thing.
A primary key is a field that contains data unique to a record
A book recommended from your professor is a reliable source of information.
Answer:
you cannot leave a field empty
you can enter data based on the defined data type
That would be persistent storage devices (non-volatile memory)
- hard disk drives (mechanical)
- solid state drives (electronic / NAND flash)
- CD (optical)
If u need more I can give u a few more
