向包含记录的现有表添加新的 NOT NULL 列
mysqlmysqli database更新于 2023/11/5 18:02:00
要向已创建的表添加新的 NOT NULL 列，请使用 ALTER 命令。让我们首先创建一个表 −
mysql> create table DemoTable -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(20) -> ); Query OK, 0 rows affected (0.60 sec)
以下是向现有表添加新的 NOT NULL 列的查询 −
mysql> alter table DemoTable add column StudentAge int NOT NULL; Query OK, 0 rows affected (0.52 sec) Records: 0 Duplicates: 0 Warnings: 0
使用 insert 插入命令在表中插入一些记录 −
mysql> insert into DemoTable(StudentName,StudentAge) values('Chris',21);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable(StudentName,StudentAge) values('David',23);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable(StudentName,StudentAge) values('Mike',NULL);
ERROR 1048 (23000): Column 'StudentAge' cannot be null
Display all records from the table using select statement −
mysql> select * from DemoTable;
这将产生以下输出 −
+-----------+-------------+------------+ | StudentId | StudentName | StudentAge | +-----------+-------------+------------+ | 1 | Chris | 21 | | 2 | David | 23 | +-----------+-------------+------------+ 2 rows in set (0.00 sec)
