MYSQL Data Types
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.)
DATE, DATETIME, TIMESTAMP, YEAR, and TIME
The DATE datatype comprises the date but no time component. Its format is 'YYYY-MM-DD' with a range of '1000-01-01' to '9999-12-31'.
The DATETIME type includes the time with a format of 'YYYY-MM-DD HH:MM:SS'. It has a range from '1000-01-01
00:00:00' to '9999-12-31 23:59:59'.
The TIMESTAMP type is an integer type comprising date and time with an effective range from '1970-01-01 00:00:01'
UTC to '2038-01-19 03:14:07' UTC.
The YEAR type represents a year and holds a range from 1901 to 2155.
The TIME type represents a time with a format of 'HH:MM:SS' and holds a range from '-838:59:59' to '838:59:59'.
Fractional Seconds (as of Version 5.6.4):