How would you add a column that only has a set choice of values?

Question

If I wanted to add a column that could only be two values, for example, a column called 'Gender' with the two possible options of 'Male' or 'Female'

Answer 1

use CHECK

Gender VARCHAR(6) NOT NULL CHECK (Gender IN ('Male', 'Female'))

SQLFiddle Demo

Answer 2

I would probably want to use a bit field type, and not allow nulls, so that value can only be 0 or 1 (true/false).