預設是空的。

除非你這個新加的列， 是 NOT NULL , 並且設定了 DEFAULT

例子程式碼如下：

mysql> create table test11(id int);

Query OK, 0 rows affected (0.01 sec)

mysql> insert into test11 values(100);

Query OK, 1 row affected (0.00 sec)

mysql> ALTER TABLE test11 ADD name varchar(10) not null default "ABC";

Query OK, 1 row affected (0.02 sec)

Records: 1 Duplicates: 0 Warnings: 0

mysql> select * from test11;

+------+------+

| id | name |

+------+------+

| 100 | ABC |

+------+------+

1 row in set (0.00 sec)