How can we apply NOT NULL constraint to a column of an existing MySQL table?

ALTER TABLE table_name MODIFY colum_name datatype NOT NULL;

mysql> Create table test123(ID INT, Date DATE); Query OK, 0 rows affected (0.19 sec) mysql> Describe test123; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | ID | int(11) | YES | | NULL | | | Date | date | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.04 sec) mysql> ALTER TABLE test123 MODIFY ID INT NOT NULL; Query OK, 0 rows affected (0.54 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> Describe test123; +-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | ID | int(11) | NO | | NULL | | | Date | date | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 2 rows in set (0.06 sec)