テーブルからカラムを削除する

alter table テーブル名 drop column 捨てるカラム名

mysql> alter table test_table drop column c_id;
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    |                |
+----------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)

mysql>