MySQL Data Types CHAR(n)
Example
CHAR(n) is a string of a fixed length of n characters. If it is CHARACTER SET utf8mb4, that means it occupies exactly 4*n bytes, regardless of what text is in it.
Most use cases for CHAR(n) involve strings that contain English characters, hence should be CHARACTER SET ascii. (latin1 will do just as good.)
country_code CHAR(2) CHARACTER SET ascii,
postal_code CHAR(6) CHARACTER SET ascii,
uuid CHAR(39) CHARACTER SET ascii, -- more discussion elsewhere
