Please tell me, google, something did not find similar questions like mine. I make a small site, it implies that there will be users who will have their avatar and description in their profile. Now I think over the database, and now the question has arisen - there are two fields, respectively, of the type ava and opisanie. The user may not have them filled in (then the default avatar is put in a stub and there will be no description). So - should I leave the NOT NULL parameter in the database for the lines, or should I put NULL? How are they in this case will be fundamentally different, and in the next if the user selects an ava, for example, I can cram a link in ava using update?