SQL_Exercise-Alter Table

desc testing_table ;
+------------+-------------+------+-----+---------+-------+
| Field      | Type        | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+-------+
| username   | varchar(30) | YES  |     | NULL    |       |
| roll_no    | int(5)      | YES  |     | NULL    |       |
| first_name | varchar(30) | YES  |     | NULL    |       |
| last_name  | varchar(30) | YES  |     | NULL    |       |
+------------+-------------+------+-----+---------+-------+

1. alter table testing _table drop column name;

2. alter table testing_table change contact_name username varchar(30);

3. alter table testing_table add(first_name varchar(30), last_name varchar(30));

4. alter table testing_table modify roll_no int(5);