如何修改现有列的数据类型?
mysqlmysqli database更新于 2025/9/16 11:24:17
要修改现有列的数据类型，您可以使用 MODIFY。让我们首先创建一个表 −
mysql> create table DemoTable ( ClientId varchar(100), ClientName varchar(100), ClientAge int, ClientProjectDeadline timestamp, ClientCountryName varchar(100), isMarried boolean, ClientNumber bigint ); Query OK, 0 rows affected (0.70 sec)
Check the description of table −
mysql> desc DemoTable;
这将产生以下输出 −
+-----------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------------------+--------------+------+-----+---------+-------+ | ClientId | varchar(100) | YES | | NULL | | | ClientName | varchar(100) | YES | | NULL | | | ClientAge | int(11) | YES | | NULL | | | ClientProjectDeadline | timestamp | YES | | NULL | | | ClientCountryName | varchar(100) | YES | | NULL | | | isMarried | tinyint(1) | YES | | NULL | | | ClientNumber | bigint(20) | YES | | NULL | | +-----------------------+--------------+------+-----+---------+-------+ 7 rows in set (0.34 sec)
现在，将列(ClientNumber)数据类型从 bigint 更改为 varchar(20) −
mysql> alter table DemoTable modify ClientNumber varchar(20); Query OK, 0 rows affected (1.82 sec) Records: 0 Duplicates: 0 Warnings: 0
让我们再次检查一下表的描述 −
mysql> desc DemoTable;
这将产生以下输出 −
+-----------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-----------------------+--------------+------+-----+---------+-------+ | ClientId | varchar(100) | YES | | NULL | | | ClientName | varchar(100) | YES | | NULL | | | ClientAge | int(11) | YES | | NULL | | | ClientProjectDeadline | timestamp | YES | | NULL | | | ClientCountryName | varchar(100) | YES | | NULL | | | isMarried | tinyint(1) | YES | | NULL | | | ClientNumber | varchar(20) | YES | | NULL | | +-----------------------+--------------+------+-----+---------+-------+ 7 rows in set (0.00 sec)
查看上面的示例输出，数据类型已从 bigint 更改为 varchar(20)。
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