mysql> CREATE DATABASE SchoolDB;
Query OK, 1 row affected (0.00 sec)
mysql> USE SchoolDB;
Database changed
mysql> create table student(xid int primary key auto_increment,xname char(10),xnage int);
Query OK, 0 rows affected (0.39 sec)
mysql> DESCRIBE student;
+-------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+----------------+
| xid | int(11) | NO | PRI | NULL | auto_increment |
| xname | char(10) | YES | | NULL | |
| xnage | int(11) | YES | | NULL | |
+-------+----------+------+-----+---------+----------------+
3 rows in set (0.02 sec)
mysql> alter table student add xaddress char(20) default 'Henan';
Query OK, 0 rows affected (0.57 sec)
mysql> DESCRIBE student;
+----------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+----------------+
| xid | int(11) | NO | PRI | NULL | auto_increment |
| xname | char(10) | YES | | NULL | |
| xnage | int(11) | YES | | NULL | |
| xaddress | char(20) | YES | | Henan | |
+----------+----------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> alter table student modify xname char(10) not null;
Query OK, 0 rows affected (2.19 sec)
mysql> DESCRIBE student;
+----------+----------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+----------------+
| xid | int(11) | NO | PRI | NULL | auto_increment |
| xname | char(10) | NO | | NULL | |
| xnage | int(11) | YES | | NULL | |
| xaddress | char(20) | YES | | Henan | |
+----------+----------+------+-----+---------+----------------+
4 rows in set (0.00 sec)