Is it good practice to set all database columns as NOT NULL?

Question

Normally is it good practice to set all database columns as NOT NULL or not ? Justify your answer.

Answer 1

No. It's a good idea to set columns to NULL where appropriate.

Answer 2

I kind of disagree with the "where appropriate" rule. It is actually rather safe to set any column to be NOT NULL; and then later modify the columns to allow NULL values when you need them. On the other hand, if you allow NULL values first and then later decide you don't want to allow them, it can potentially be much more difficult to do this.

It may make your database table/column descriptions quite ugly if you do this excessively, but when in doubt, go ahead and restrict the data.