mysql> create table t_zhyou110z (
    ->  userid int primary key,
    ->  password varchar(10)
    -> );
Query OK, 0 rows affected (0.13 sec)

mysql> desc t_zhyou110z;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| userid   | int(11)     | NO   | PRI | NULL    |       |
| password | varchar(10) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.11 sec)

-- 修改password 为not null / ACMAIN
mysql> alter table t_zhyou110z modify password varchar(10) not null;
Query OK, 0 rows affected (0.22 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc t_zhyou110z;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| userid   | int(11)     | NO   | PRI | NULL    |       |
| password | varchar(10) | NO   |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql>

------解决方案--------------------
探讨

3Q 还是你们呢 这样写还可以长度 要修改类型怎么写呢