添加一个char字段：
mysql> alter table stock add src char(20);
Query OK, 3766 rows affected (0.65 sec)
Records: 3766 Duplicates: 0 Warnings: 0
添加一个datatime字段：
mysql> alter table stock add ctime datetime not null;
Query OK, 3766 rows affected (0.27 sec)
Records: 3766 Duplicates: 0 Warnings: 0
查看表定义：
mysql> desc stock;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int(11) | NO | PRI | | |
| code | char(6) | YES | | NULL | |
| name | char(10) | YES | | NULL | |
| utime | datetime | YES | | NULL | |
| src | char(20) | YES | | NULL | |
| ctime | datetime | NO | | | |
+-------+----------+------+-----+---------+-------+
6 rows in set (0.05 sec)
--2020年5月3日--