在单个 MySQL 查询中使用 ALTER 向现有表添加新列和索引?
mysqlmysqli database
要向现有表添加新列，请使用 ADD。然后，要添加新索引，请使用 ADD INDEX()。让我们首先创建一个表 −
mysql> create table DemoTable -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(100), -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.69 sec)
让我们检查一下表的描述 −
mysql> desc DemoTable;
这将产生以下输出 −
+-------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+--------------+------+-----+---------+----------------+ | Id | int(11) | NO | PRI | NULL | auto_increment | | Name | varchar(100) | YES | | NULL | | +-------+--------------+------+-----+---------+----------------+ 2 rows in set (0.01 sec)
这是向现有表添加新列和索引的查询 −
mysql> alter table DemoTable -> add ArrivalDate DATETIME DEFAULT NOW(), -> add index(ArrivalDate); Query OK, 0 rows affected (2.05 sec) Records: 0 Duplicates: 0 Warnings: 0
让我们再次检查一下该表的描述 −
mysql> desc DemoTable;
这将产生以下输出 −
+-------------+--------------+------+-----+-------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------------+--------------+------+-----+-------------------+----------------+ | Id | int(11) | NO | PRI | NULL | auto_increment | | Name | varchar(100) | YES | | NULL | | | ArrivalDate | datetime | YES | MUL | CURRENT_TIMESTAMP | | +-------------+--------------+------+-----+-------------------+----------------+ 3 rows in set (0.01 sec)
