> A properly normalized database would put emails in another table and reference them using a key. You'll have no empty columns. You'll know there is no email b

> A properly normalized database would put emails in another table and reference them using a key. You'll have no empty columns. You'll know there is no email because there is no value, not because there's a NULL value. A table with 2 columns (key, value) is logically equivalent to a nullable column in the parent table. There are times when a separate table is a good solution. But there are also times, for example if you have a lot of optional columns that cannot be grouped into sets, that such a thing would be massively over-complicated, space wasting, and poor performing.