mysql> select * from ttt;
+----+------+
| id | col2 |
+----+------+
| 1 | NULL |
+----+------+
1 row in set (0.00 sec)
如果default 不为''
mysql> create table ttt(id int primary key, col2 text not null default 'abc');
ERROR 1101 (42000): BLOB/TEXT column 'col2' can't have a default value