SQL テーブルのカラム情報取得

# テーブルのカラム情報取得
## クエリ
```sql
show columns from [テーブル名];
show full columns from [テーブル名]; -- ←コメントまで取得したい場合
```

## 実行結果
```sql
mysql> show columns from users;
+---------------+--------------+------+-----+---------+----------------+
| Field         | Type         | Null | Key | Default | Extra          |
+---------------+--------------+------+-----+---------+----------------+
| id            | int(11)      | NO   | PRI | NULL    | auto_increment |
| name_sei      | varchar(255) | NO   |     | NULL    |                |
| name_mei      | varchar(255) | NO   |     | NULL    |                |
| tel           | varchar(255) | YES  |     | NULL    |                |
| email         | varchar(255) | NO   | MUL | NULL    |                |
| postal_code   | varchar(255) | YES  |     | NULL    |                |
| address       | varchar(255) | YES  |     | NULL    |                |
| created       | datetime     | NO   |     | NULL    |                |
| modified      | datetime     | NO   |     | NULL    |                |
+---------------+--------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)
```

```sql
mysql> show full columns from users;
+---------------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+--------------+
| Field         | Type         | Collation       | Null | Key | Default | Extra          | Privileges                      | Comment      |
+---------------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+--------------+
| id            | int(11)      | NULL            | NO   | PRI | NULL    | auto_increment | select,insert,update,references |              |
| name_sei      | varchar(255) | utf8_general_ci | NO   |     | NULL    |                | select,insert,update,references | ユーザー名の姓 |
| name_mei      | varchar(255) | utf8_general_ci | NO   |     | NULL    |                | select,insert,update,references | ユーザー名の名 |
| tel           | varchar(255) | utf8_general_ci | YES  |     | NULL    |                | select,insert,update,references | 電話番号      |
| email         | varchar(255) | utf8_general_ci | NO   | MUL | NULL    |                | select,insert,update,references | メールアドレス  |
| postal_code   | varchar(255) | utf8_general_ci | YES  |     | NULL    |                | select,insert,update,references | 郵便番号      |
| address       | varchar(255) | utf8_general_ci | YES  |     | NULL    |                | select,insert,update,references | 住所         |
| created       | datetime     | NULL            | NO   |     | NULL    |                | select,insert,update,references |              |
| modified      | datetime     | NULL            | NO   |     | NULL    |                | select,insert,update,references |              |
+---------------+--------------+-----------------+------+-----+---------+----------------+---------------------------------+--------------+
9 rows in set (0.00 sec)
```

# その他
## 既存カラムにコメント追加
```sql
ALTER TABLE [テーブル名] CHANGE COLUMN [カラム名] [カラム名] [型] [制約系(例: NOT NULL, DEFAULT 'aaa', etc...)] COMMENT [コメント];
```

## auto_incrementの追加
```sql
alter table [テーブル名] auto_increment = [id];
```