Question

I’ve never used null before really, I tend to avoid using it and having it existing in my data. However I recently designed this table (simplified):

tblPeopleWhoNeedToCastVotes
User |  hasVotedYes

In this scenario, hasVotedYes can either be null, true or false. Null indicates they have not yet cast their vote (useful information).

Is this bad practise or fine?

Answer 1

This is really what NULL is intended for – where the data is not available. From Wikipedia:

Null is a special marker used in Structured Query Language (SQL) to indicate that a data value does not exist in the database.

I wouldn’t recommend using it as a general “third option”, I’d go with a tinyint and map it to an Enum in code instead. However, for Yes/No and an Unknown, I’d say a NULL is probably the best way, as reading 0/1/2 in the database would be less clear.