MySQL:

LAST_DAY

Syntax:
LAST_DAY(date)

Takes a date or datetime value and returns the corresponding value for
the last day of the month. Returns NULL if the argument is invalid.

Example

mysql> SELECT LAST_DAY('2003-02-05');
-> '2003-02-28'
mysql> SELECT LAST_DAY('2004-02-05');
-> '2004-02-29'
mysql> SELECT LAST_DAY('2004-01-01 01:01:01');
-> '2004-01-31'
mysql> SELECT LAST_DAY('2003-03-32');
-> NULL

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