mysql> desc t1;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a     | bit(1)     | YES  |     | NULL    |       |
| b     | tinyint(4) | YES  |     | NULL    |       |
| c     | binary(1)  | YES  |     | NULL    |       |    #binary默认显示宽度为1
+-------+------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> alter table t1 modify c binary(30);#修改显示宽度为30
Query OK, 5 rows affected (0.04 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> select * from t1;#查询发现修改binary显示宽度前的列还是仅显示第一个字母,也就是显示宽度为1
+------+------+--------------------------------+
| a    | b    | c                              |
+------+------+--------------------------------+
|     | -127 | NULL                           |
|     |  127 | NULL                           |
|      |   28 | NULL                           |
|     |   18 | NULL                           |
|      |   10 | m                              |
+------+------+--------------------------------+
5 rows in set (0.00 sec)

mysql> insert into t1 values(0,25,'mama haha');#再次插入数据
Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;
+------+------+--------------------------------+
| a    | b    | c                              |
+------+------+--------------------------------+
|     | -127 | NULL                           |
|     |  127 | NULL                           |
|      |   28 | NULL                           |
|     |   18 | NULL                           |
|      |   10 | m                              |
|      |   25 | mama haha                      |  #再次插入新行,全部binary列值显示出来
+------+------+--------------------------------+
6 rows in set (0.00 sec)

mysql> insert into t1 values(0,18,'the best one is you');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t1;
+------+------+--------------------------------+
| a    | b    | c                              |
+------+------+--------------------------------+
|     | -127 | NULL                           |
|     |  127 | NULL                           |
|      |   28 | NULL                           |
|     |   18 | NULL                           |
|      |   10 | m                              |
|      |   25 | mama haha                      |
|      |   18 | the best one is you            |
+------+------+--------------------------------+
7 rows in set (0.01 sec)