Add values in a new column in a pre-existing table

Question

Suppose I add a new column in a table and I have to add values to all of them at once. How can I do that?
Using Update and Set command I am able to add only one at a time.

Answer 1

if same value need to update..you can update by

update Customer
set xyz = 123

where xyz = isnull

Answer 2

Or set a Default value within the new column when creating it if you can. This will only work if it doesn't need to be different or unique for each row.

Answer 3

No the values are different. Let’s say I have created a table named student and I need to add fees of the students. Using Alter command I add fees but how do I add different values for each student