The constant starts with "D" and is framed in single quotes. You may also use truncated values without date, or without time, or just as an empty value. The range of values is from January 1, 1970 through December 31, 2037. The values of constants and variables of datetime type take 4 bytes in the computer memory. A value represents the amount of seconds elapsed from 00:00 of January 1, 1970.