テーブルにカラムを追加する

alter table テーブル名 add column 新しいカラム名 型情報;

mysql> alter table test_table add column c_id tinyint not null;
Query OK, 27 rows affected (0.02 sec)
Records: 27  Duplicates: 0  Warnings: 0

mysql> desc test_table;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| topic_id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name        | varchar(48) | YES  |     | NULL    |                |
| c_id        | tinyint(11) | NO   |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)