In reality its a boleean
so bit is fine just have to decide
0 = Male, 1 = Femaleor 1 = Male, 0 = Female
Char(1)M (Male)F (Female)U (Unknown)B (Both)
i typically use a char(1) with a check constraint to allow only two values:
ie ALTER TABLE BLAH ADD GENDER CHAR(1) NULL CHECK (GENDER='M' OR GENDER='F')
Null is unknown. That is the purpose of null.
>Char(1)>M (Male)>F (Female)>U (Unknown)>B (Both)