MySQL Modify column type :

    The modify statement is also used to change the column type in a table, as the previous example. The below query will modify the column type.

mysql> alter table student modify name varchar(40);
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc student;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| studid  | int(10)     | YES  |     | NULL    |       |
| name    | varchar(40) | YES  |     | NULL    |       |
| marks   | int(10)     | YES  |     | NULL    |       |
| address | varchar(40) | YES  |     | NULL    |       |
| phone   | int(10)     | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)