（改）修改、更新数据表中的数据记录
UPDATE表名 SET 字段名1=字段值1，[字段名2=字段值2] [WHERE 条件表达式]；
MySQL [mysql_chuid]> insert into student(id,name,sex)values(1,'chd','man');
Query OK, 1 row affected (0.00 sec)
MySQL [mysql_chuid]> insert into student(id,name,sex)values(2,'chuid','man');
Query OK, 1 row affected (0.02 sec)
MySQL [mysql_chuid]> insert into student(id,name,sex)values(3,'anivd','man'); # 添加三行新内容
Query OK, 1 row affected (0.02 sec)
MySQL [mysql_chuid]> select * from student; # 查询student表中所有的数据信息
+----+-------+------+
| id | name | sex |
+----+-------+------+
| 1 | chd | man |
| 2 | chuid | man |
| 3 | anivd | man |
+----+-------+------+
3 rows in set (0.00 sec)
MySQL [mysql_chuid]> update students set id=5 where name_list='anivd'; # 将name_list=anivd的id改为5
Query OK, 1 row affected (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MySQL [mysql_chuid]> select * from students;
+----+-----------+------+
| id | name_list | sex |
+----+-----------+------+
| 1 | chd | man |
| 2 | chuid | man |
| 5 | anivd | man |
+----+-----------+------+
4 rows in set (0.00 sec)
（改）修改表名
ALTER TABLE旧表名 RENAME 新表名；
MySQL [mysql_chuid]> alter table student rename students;
Query OK, 0 rows affected (0.00 sec)
MySQL [mysql_chuid]> show tables;
+-----------------------+
| Tables_in_mysql_chuid |
+-----------------------+
| students |
+-----------------------+
1 row in set (0.00 sec)
（改）扩展表结构 [增加字段]
ALTER TABLE表名 ADD address varchar(50) default ‘’；
MySQL [mysql_chuid]> select * from student;
+----+-------+
| id | name |
+----+-------+
| 1 | chd |
| 2 | chuid |
| 3 | anivd |
+----+-------+
3 rows in set (0.00 sec)
MySQL [mysql_chuid]> alter table student add sex char(3) default 'man'; # 增加表的字段
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0
MySQL [mysql_chuid]> select * from student;
+----+-------+------+
| id | name | sex |
+----+-------+------+
| 1 | chd | man |
| 2 | chuid | man |
| 3 | anivd | man |
+----+-------+------+
3 rows in set (0.00 sec)
（改）修改字段（列）名，添加唯一键
ALTER TABLE表名 CHANGE 旧字段名 新字段名 新数据类型 [unique key];
1）旧字段名：指修改前的字段名；
2）新字段名：指修改后的字段名；
3）新数据类型：指修改后的数据类型，如果不需要修改字段的数据类型，可以将新数据类型设置成与原来一样，但数据类型不能为空。
4）unique key : 唯一键（唯一键的作用：是为了解决表中字段需要具有唯一性的问题，也就是说唯一键的这个字段只会有一个）
# 修改表名students的字段name为name_list
MySQL [mysql_chuid]> alter table students change name name_list varchar(10) unique key;
Query OK, 3 rows affected (0.09 sec)
Records: 3 Duplicates: 0 Warnings: 0
MySQL [mysql_chuid]> select * from students;
+----+-----------+------+
| id | name_list | sex |
+----+-----------+------+
| 1 | chd | man |
| 2 | chuid | man |
| 3 | anivd | man |
+----+-----------+------+
3 rows in set (0.01 sec)
MySQL [mysql_chuid]> insert into students(id,name_list,sex)values(5,'chen','man'); # 创建内容，指定name_list为chen
Query OK, 1 row affected (0.00 sec)
MySQL [mysql_chuid]> select * from students;
+----+-----------+------+
| id | name_list | sex |
+----+-----------+------+
| 1 | chd | man |
| 2 | chuid | man |
| 3 | anivd | man |
| 5 | chen | man |
+----+-----------+------+
4 rows in set (0.00 sec)
MySQL [mysql_chuid]> insert into students(id,name_list,sex)values(6,'chen','man'); # 再次想创建name_list为chen就会报错
ERROR 1062 (23000): Duplicate entry 'chen' for key 'name_list'
（改）修改字段数据类型
修改字段的数据类型就是把字段的数据类型转换成另一种数据类型。
修改字段数据类型的语法格式：ALTER TABLE <表名> MODIFY <字段名> <数据类型>
1）表名：指要修改数据类型的字段所在表的名称；
2）字段名：指需要修改的字段；
3）数据类型：指修改后字段的新数据类型。
MySQL [mysql_chuid]> desc class_1;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| claID | int(5) | YES | | NULL | |
| id | int(5) | YES | | NULL | |
| name | char(10) | YES | | NULL | |
| hometown | varchar(20) | YES | | NULL | |
| sex | int(5) | YES | | NULL | |
| age | int(5) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
6 rows in set (0.01 sec)
MySQL [mysql_chuid]> ALTER table class_1 MODIFY name varchar(15); # 将name字段的数据类型改为VARCHAR（15）
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0
MySQL [mysql_chuid]> desc class_1;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| claID | int(5) | YES | | NULL | |
| id | int(5) | YES | | NULL | |
| name | varchar(15) | YES | | NULL | |
| hometown | varchar(20) | YES | | NULL | |
| sex | int(5) | YES | | NULL | |
| age | int(5) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
6 rows in set (0.00 sec)