Using a foreign key - only 2 records?

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Should I use a foreign key for "balanceimpact" that only has two options either "CREDIT" or "DEBIT"?

Does it even make sense, there are only two options here?

It's not so much as how many options there are, but what kind of rel this is (1:1; 1:n; etc).

On this particular case, I wouldn't use a foreign key, just leave it as a column.

Also, as Marc_S suggested on his comment, add a CHECK constraint to ensure that only one of those 2 values are entered.

ALTER TABLE your_table
ADD CONSTRAINT chk_balanceimpact CHECK (balanceimpact in ('C','D'))
GO

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