Linux环境下数据库的学习总结（一）
该篇讲 mysql 的基本使用
启动MySQL
在Linux内安装好MySQL后，使用根用户才能进行操作
//进入根用户操作命令
[centos6@bogon ~]$su //输入su
Password: // 输入密码
[root@bogon centos6]# service mysqld start //服务器启动指令
Starting mysqld: [ OK ] //提示启动成功
[root@bogon centos6]# mysql //打开MySQL
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.1.73 Source distribution
Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> //可输入命令行查看，创建数据库指令
查看数据库
命令：
show databases; //在结束部分一定要加分号（英文）mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| LLL |
| mysql |
| red_A2 |
| test |
+--------------------+ //显示当前您所拥有的数据库
5 rows in set (0.09 sec)
创建一个数据库
命令：
create database + 库名 ;mysql> create database LIU;
Query OK, 1 row affected (0.00 sec)
结果可以用之前的查看数据库命令来看到
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| LIU //新建的数据库 |
| LLL |
| mysql |
| red_A2 |
| test |
+--------------------+
对于数据库内的使用，查看与创建表格
数据库的使用
命令:
use + 想使用的数据库库名;
mysql> use LIU;
Database changed
在当前数据库下创建表格
命令: create table + 表名(
列名 + 类型 ,
列名 + 类型 ，
...）；
**注意在最后定义的列名加类型后不需要用逗号**mysql> create table students (
-> name varchar(20),
-> english float(4,2),
-> chinese float(4,2),
-> math float(4,2));
Query OK, 0 rows affected (0.04 sec)建表完成后可以用 desc+ 表名 语句查看表的基本信息
mysql> desc students;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| english | float(4,2) | YES | | NULL | |
| chinese | float(4,2) | YES | | NULL | |
| math | float(4,2) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
//表的基本信息在此在表中插入数据
命令：
insert into + 表名 values('字符型',数字型);
mysql> insert into students values('Linda',79,88,92);
Query OK, 1 row affected (0.00 sec)
//可多次插入大量数据，但是得保持格式一致
mysql> insert into students values('Ana',91,77,66);
Query OK, 1 row affected (0.00 sec)
mysql> insert into students values('Paco',89,87,76);
Query OK, 1 row affected (0.00 sec)
mysql> insert into students values('Rob',96,57,76);
Query OK, 1 row affected (0.00 sec)
查看表格
命令：
select*from + 表名;
+-------+---------+---------+-------+
| name | english | chinese | math |
+-------+---------+---------+-------+
| Linda | 79.00 | 88.00 | 92.00 |
| Ana | 91.00 | 77.00 | 66.00 |
| Paco | 89.00 | 87.00 | 76.00 |
| Rob | 96.00 | 57.00 | 76.00 |
+-------+---------+---------+-------+
4 rows in set (0.00 sec)
对表格进简单的删添与更改工作
修改表
命令：
alter table + 表名
add(列名 数据类型); //添加
alter table + 表名
modify(列名 数据类型); //更改
alter table + 表名
drop(列名) ; //删除该列添加列
mysql> alter table students add history float(4,2) after name;
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
\\在学生姓名后面添加一列历史成绩
mysql> select * from students;
+-------+---------+---------+---------+-------+
| name | history | english | chinese | math |
+-------+---------+---------+---------+-------+
| Linda | NULL | 79.00 | 88.00 | 92.00 |
| Ana | NULL | 91.00 | 77.00 | 66.00 |
| Paco | NULL | 89.00 | 87.00 | 76.00 |
| Rob | NULL | 96.00 | 57.00 | 76.00 |
+-------+---------+---------+---------+-------+
4 rows in set (0.00 sec)
mysql> desc students;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| history | float(4,2) | YES | | NULL | |
| english | float(4,2) | YES | | NULL | |
| chinese | float(4,2) | YES | | NULL | |
| math | float(4,2) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
修改某列信息
mysql> alter table students modify history int;
Query OK, 4 rows affected (0.01 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from students;
+-------+---------+---------+---------+-------+
| name | history | english | chinese | math |
+-------+---------+---------+---------+-------+
| Linda | NULL | 79.00 | 88.00 | 92.00 |
| Ana | NULL | 91.00 | 77.00 | 66.00 |
| Paco | NULL | 89.00 | 87.00 | 76.00 |
| Rob | NULL | 96.00 | 57.00 | 76.00 |
+-------+---------+---------+---------+-------+
4 rows in set (0.00 sec)
mysql> desc students;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| history | int(11) | YES | | NULL | |
| english | float(4,2) | YES | | NULL | |
| chinese | float(4,2) | YES | | NULL | |
| math | float(4,2) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
//将历史成绩数据类型从浮点型更改为整型删除某列
mysql> alter table students drop history;
Query OK, 4 rows affected (0.01 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from students;
+-------+---------+---------+-------+
| name | english | chinese | math |
+-------+---------+---------+-------+
| Linda | 79.00 | 88.00 | 92.00 |
| Ana | 91.00 | 77.00 | 66.00 |
| Paco | 89.00 | 87.00 | 76.00 |
| Rob | 96.00 | 57.00 | 76.00 |
+-------+---------+---------+-------+
4 rows in set (0.00 sec)
mysql> desc students;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | varchar(20) | YES | | NULL | |
| english | float(4,2) | YES | | NULL | |
| chinese | float(4,2) | YES | | NULL | |
| math | float(4,2) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
//将历史成绩这一列完全删除