在单个MySQL查询中使用ALTER向现有表添加新列和索引？
要将新列添加到现有表中，请使用ADD。这样，要添加新索引，请使用ADDINDEX()。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) -> );
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 | +-------+--------------+------+-----+---------+----------------+ | 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); 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 | +-------------+--------------+------+-----+-------------------+----------------+ | 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)