【MySQL篇】表的操作
1，创建表
语法：
create table (
field1 datatype,
field2 datatype,
field3 datatype
)charset 字符集 collate 校验规则 engine 存储引擎;
说明：
- field表示列名
- datatype表示列的类型
- charset字符集，如果没有指明，则以所在数据库的字符集为准
- collate校验规则，如果没有指明，则以所在数据库的校验规则为准
示例：
mysql> use study1;//进入数据库
Database changed
mysql> create table user1( //建表
-> id int,
-> name varchar(20),
-> password varchar(32),
-> birthday date
-> )charset utf8 engine MyISAM;
Query OK, 0 rows affected, 1 warning (0.01 sec)
不同的存储引擎，创建表的文件不一样 。user1表的存储引擎是MyISAM，在数据目录中的文件如下图：
root@hcss-ecs-982b:/var/lib/mysql/study1# ll
total 16
drwxr-x--- 2 mysql mysql 4096 Feb 26 15:32 ./
drwx------ 8 mysql mysql 4096 Feb 26 15:29 ../
-rw-r----- 1 mysql mysql 3954 Feb 26 15:32 user1_365.sdi
-rw-r----- 1 mysql mysql 0 Feb 26 15:32 user1.MYD
-rw-r----- 1 mysql mysql 1024 Feb 26 15:32 user1.MY
2，查看表结构
desc 表名;
mysql> desc user1;//查看表 索引类型 扩充
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| birthday | date | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
// 字段名字 字段类型 是否允许为空 默认值3，修改表
修改表的结构，比如字段名称，字段大小，字段类型，表的字符集，表的存储引擎等等 。还有需求添加字段，删除字段等。
先往user1表中插入 一些数据：
mysql> insert into user1 values (1,'a','b','2025-01-01'), (2,'b','c','2025-022-26');//插入数据
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from user1;
+------+------+----------+------------+
| id | name | password | birthday |
+------+------+----------+------------+
| 1 | a | b | 2025-01-01 |
| 2 | b | c | 2025-02-26 |
+------+------+----------+------------+
2 rows in set (0.00 sec)- 在user表中增加一个字段，来保存图片路径：
mysql> desc user1;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| birthday | date | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
mysql> alter table user1 add assets varchar(100) after birthday;//birthday后添加一个assets字段
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc user1;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| assets | varchar(100) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)- 修改name，将其长度改为60
mysql> alter table user1 modify name varchar(60);
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc user1;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(60) | YES | | NULL | |
| password | varchar(32) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| assets | varchar(100) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)- 删除password列
注意：删除字段，其对应的列信息也就没有了
mysql> alter table user1 drop password;
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc user1;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(60) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| assets | varchar(100) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
4 rows in set (0.01 sec)- 修改表明为empoyee
mysql> alter table user1 rename to employee;
Query OK, 0 rows affected (0.01 sec)
mysql> desc employee;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| name | varchar(60) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| assets | varchar(100) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
4 rows in set (0.01 sec)
注意：to可以省略掉
- 将name列需改为xingming
mysql> alter table employee change name xingming varchar(20);//需要完整的定义
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> desc employee;
+----------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id | int | YES | | NULL | |
| xingming | varchar(20) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| assets | varchar(100) | YES | | NULL | |
+----------+--------------+------+-----+---------+-------+
4 rows in set (0.00 sec)4，删除表
drop table 表名;
mysql> drop table employee;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
Empty set (0.00 sec)