１カラムの削除
MariaDB [test]> select *from meibo;
+------+------+--------+----------+------+
| No | id | name | category | flag |
+------+------+--------+----------+------+
| NULL | 1 | 佐藤 | NULL | NULL |
| NULL | 2 | suzuki | NULL | NULL |
| NULL | 3 | 山口 | NULL | NULL |
+------+------+--------+----------+------+
「category」を削除
MariaDB [test]> ALTER TABLE meibo DROP COLUMN category;
MariaDB [test]> select *from meibo;
+------+------+--------+------+
| No | id | name | flag |
+------+------+--------+------+
| NULL | 1 | 佐藤 | NULL |
| NULL | 2 | suzuki | NULL |
| NULL | 3 | 山口 | NULL |
+------+------+--------+------+