Date values with two-digit years are ambiguous because the century is unknown. Such values must be interpreted into four-digit form because MySQL stores years internally using four digits.

For DATETIME, DATE, TIMESTAMP, and YEAR types, MySQL interprets dates specified with ambiguous year values using these rules:

Remember that these rules are only heuristics that provide reasonable guesses as to what your data values mean. If the rules used by MySQL do not produce the values you require, you must provide unambiguous input containing four-digit year values.

In MySQL, the YEAR data type can store the years 0 and 1901 to 2155 in one byte and display them using two or four digits. For input, all two-digit years are considered to be in the range 1970 to 2069, which means that if you store 01 in a YEAR column, MySQL Server treats it as 2001.

ORDER BY properly sorts YEAR values that have two-digit years.

Some functions like MIN() and MAX() convert a YEAR to a number. This means that a value with a two-digit year does not work properly with these functions. The fix in this case is to convert the YEAR to four-digit year format.