版权声明:from 瑾川(fakehydra.xyz) https://blog.csdn.net/fake_hydra/article/details/83348928
数据库 数据类型
创建表
MariaDB [oldboy]> CREATE TABLE student(sid INT,sname VARCHAR(20),sage TINYINT,sgender ENUM('m','f'),scomtime DATETIME);
--int 整数 -2^31 ~ 3^31-1
--varchar(20) 变长
--char(20) 定长
--tinyint 整数 255
--ENUM(‘m’,‘f’) 枚举类型 (男,女)
--datetime 时间类型 年月日时分秒
show create table stu;
| stu | CREATE TABLE `stu` (
`sid` int(11) NOT NULL AUTO_INCREMENT COMMENT '学号',
`sname` varchar(20) NOT NULL COMMENT '姓名',
`sage` tinyint(3) unsigned DEFAULT NULL COMMENT '年龄',
`sgender` enum('m','f') DEFAULT 'm' COMMENT '性别',
`scomtime` datetime NOT NULL COMMENT '入学时间',
PRIMARY KEY (`sid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
以下选项会影响到数据的录入
-- not null 非空的
--primary key 唯一且非空的
--auto_increment 自增长 需要有 primary key 或者unique key
--default 默认值
--unsigned 非负数
--comment ‘xx’ 注释
show tables; --查看当前数据库下所有表
show create table --查看表的创建语句
desc stu; --查看表中列的定义信息
修改表定义
重命名表名
MariaDB [oldboy]> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| stu |
| student |
+------------------+
MariaDB [oldboy]> ALTER TABLE stu RENAME stt;
MariaDB [oldboy]> show tables;
+------------------+
| Tables_in_oldboy |
+------------------+
| stt |
| student |
+------------------+
2 rows in set (0.00 sec)
添加列
MariaDB [oldboy]> desc stt;
+----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------------+------+-----+---------+----------------+
| sid | int(11) | NO | PRI | NULL | auto_increment |
| sname | varchar(20) | NO | | NULL | |
| sage | tinyint(3) unsigned | YES | | NULL | |
| sgender | enum('m','f') | YES | | m | |
| scomtime | datetime | NO | | NULL | |
+----------+---------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
MariaDB [oldboy]> alter table stt add stest int;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
MariaDB [oldboy]> desc stt;
+----------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------------+------+-----+---------+----------------+
| sid | int(11) | NO | PRI | NULL | auto_increment |
| sname | varchar(20) | NO | | NULL | |
| sage | tinyint(3) unsigned | YES | | NULL | |
| sgender | enum('m','f') | YES | | m | |
| scomtime | datetime | NO | | NULL | |
| stest | int(11) | YES | | NULL | |
+----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)