ISO 3166-1 alpha-3 code

An alpha-3 code names the same country as the two-letter code, in a form that is easier to read without a lookup table: BRA is recognizable where BR is not.

It carries no information the alpha-2 code lacks. Which of the two a dataset uses is a matter of convention, so a country may need both stored.

Letters are not always the first two of the alpha-3 code, so the codes cannot be derived from each other and have to be read from the standard.