将MySQL列更改为具有NOT NULL约束
要更新约束，请使用MODIFY命令。以下是语法-
alter table yourTableName modify yourExistingColumnName yourExistingDataType NOT NULL;
让我们首先创建一个表-
mysql> create table DemoTable -> ( -> UserId int NOT NULL AUTO_INCREMENT, -> UserFirstName varchar(100), -> UserLastName varchar(100), -> UserEmailId varchar(100), -> UserPassword varchar(100), -> PRIMARY KEY(UserId) -> ); Query OK, 0 rows affected (0.91 sec)
以下是将列的约束更改为NOTNULL的查询-
mysql> alter table DemoTable modify UserFirstName varchar(100) NOT NULL; Query OK, 0 rows affected (2.13 sec) Records: 0 Duplicates: 0 Warnings: 0
让我们使用desc命令检查列是否具有NOTNULL约束-
mysql> desc DemoTable;
输出结果
这将产生以下输出。现在UserFirstName列具有NOTNULL约束-
+---------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+--------------+------+-----+---------+----------------+ | UserId | int(11) | NO | PRI | NULL | auto_increment | | UserFirstName | varchar(100) | NO | | NULL | | | UserLastName | varchar(100) | YES | | NULL | | | UserEmailId | varchar(100) | YES | | NULL | | | UserPassword | varchar(100) | YES | | NULL | | +---------------+--------------+------+-----+---------+----------------+ 5 rows in set (0.17 sec)