MySQL:

DATEDIFF

Syntax:
DATEDIFF(expr1,expr2)

DATEDIFF() returns expr1 ? expr2 expressed as a value in days from
one date to the other. expr1 and expr2 are date or date-and-time
expressions. Only the date parts of the values are used in the
calculation.

Example

mysql> SELECT DATEDIFF('2007-12-31 23:59:59','2007-12-30');
-> 1
mysql> SELECT DATEDIFF('2010-11-30 23:59:59','2010-12-31');
-> -31

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