it's unreasonable. NULL isn't a value, it means, "the value can't be known". If a primary key of a table has part of it that is unknown, you've designed your

it's unreasonable. NULL isn't a value, it means, "the value can't be known". If a primary key of a table has part of it that is unknown, you've designed your schema completely incorrectly, and you should brush up on normal form: http://en.wikipedia.org/wiki/Database_normalization#Normal_forms http://en.wikipedia.org/wiki/Database_normalization#Normal_f...