我们如何将NOT NULL约束应用于现有MySQL表的列？
我们可以借助ALTERTABLE语句将NOTNULL约束应用于现有MySQL表的列。
语法
ALTER TABLE table_name MODIFY colum_name datatype NOT NULL;
示例
mysql> Create table test123(ID INT, Date DATE); 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; 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)