We can use 2-digit year value either in single date expression or in both date expressions used as argument/s in MySQL DATEDIFF() function.
For example, the query below is using 2-digit year value in first date expression and other is having 4-digit year value.
mysql> Select DATEDIFF('18-10-22','2017-10-22'); +-----------------------------------+ | DATEDIFF('18-10-22','2017-10-22') | +-----------------------------------+ | 365 | +-----------------------------------+ 1 row in set (0.00 sec)
And the query below is using 2-digit year value in both date expressions.
mysql> Select DATEDIFF('18-10-22','17-10-22'); +---------------------------------+ | DATEDIFF('18-10-22','17-10-22') | +---------------------------------+ | 365 | +---------------------------------+ 1 row in set (0.00 sec)