primary keys

Hello everyone,

How would you create primary keys in personal oracle 7.3 using the create sequence route?
Also I would like my pk's to be informative (e.g.) customer order id # is today's date + order number

The second case would be creating a pk that uses the concatenation of the first four letters of the fname and the first 4 letters of the lname.

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Thanks & have a nice day!  ;-)