如何将NOT NULL约束添加到已创建的MySQL列?
使用ALTER TABLE实现此目的。让我们首先创建一个表-
mysql> create table DemoTable -> (
-> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> StudentName varchar(100)
-> );
让我们检查表的描述-
mysql> desc DemoTable;
这将产生以下输出-
+-------------+--------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| StudentId | int(11) | NO | PRI | NULL | auto_increment |
| StudentName | varchar(100) | YES | | NULL | |
+-------------+--------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
这是将NOT NULL约束添加到另一列“ StudentName”的查询,该约束最初并未设置为NOT NULL-
mysql> alter table DemoTable modify StudentName varchar(100) NOT NULL;Records: 0 Duplicates: 0 Warnings: 0
让我们再次检查表的描述-
mysql> desc DemoTable;
这将产生以下输出-
+-------------+--------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| StudentId | int(11) | NO | PRI | NULL | auto_increment |
| StudentName | varchar(100) | NO | | NULL | |
+-------------+--------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
以上是 如何将NOT NULL约束添加到已创建的MySQL列? 的全部内容, 来源链接: utcz.com/z/331391.html