Oracle: If a unique key constraint on DATE column is created, will it validate the rows that are inserted with sysdate?

Question

I am using below statement but i got error.
ALTER TABLE XXXtable
ADD xxx_name varchar2(50) not null;

error message:
ORA-01758: table must be empty to add mandatory (NOT NULL) column

Answer 1

It won't, Because SYSDATE format contains time attached with it.

Answer 2

UNIQUE CONSTARINT CAN VALIDATE PSEUDOCLOUMN SYSDATE

SYSDATE FORMAT IS LIKE 3/2/2010 8:42:46 PM

SO FOR EACH MILLISECOND IF U INSER A ROW IT WILL TAKE THE INSERTION BUT IF U INSERT IN EACH FRACTION OF MILLISECOND ITS VALIDATE AND UNIQUE CONSTARINT IS VOILATED.

or

If there is a unique key defined on a column which has date as the data type then one can insert the same date more than once.The date is always stored in the format dd-mon-yyyy hh:mi:ss.The reason why it will accept the same date again is that the time taken for you to enter the date for the first time and entering the date again for the second time there will be a gap of atleast one secon which makes that date value unique. ONE CAN INSERT THE SAME DATE VALUE IN A UNIQUE COLUMN MORE THAN ONCE.

Comments

It won't, Because SYSDATE format contains time attached with it.