数据库上手避坑之--探索数据库

一、数据库的登陆：当使用mysql -usqlxxl -p登陆数据库的那一刻，到数据库操作提示符MariaDB [(none)]>的出现，就是数据库的登陆过程

mysql -usqlxxl -p
Enter password: 
Welcome to the MariaDB monitor.  Commands end with ; or g.
Your MariaDB connection id is 3
Server version: 10.5.8-MariaDB Arch Linux

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

MariaDB [(none)]>

二、基本概念：数据库主要靠表来存储数据。表的主要元素有属性，一个属性为一列，所有的属性构成列的集合。每一行数据的每一个列都有数据。反映着用户查看数据的方式。

　　数据库：存储数据表的库为数据库。表必须在数据库中。

　　数据库的操作主要有应用、查看、创建和删除。

MariaDB [(none)]> show databases;　　　　　　　　　　//显示数据库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student_info       |
+--------------------+
4 rows in set (0.036 sec)

MariaDB [(none)]> create database sample;　　　　　　//创建数据库
Query OK, 1 row affected (0.000 sec)

MariaDB [(none)]> show databases;　　　　　　　　　　//查看数据库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sample             |
| student_info       |
+--------------------+
5 rows in set (0.001 sec)

MariaDB [(none)]> drop database sample;　　　　　　　　//删除数据库
Query OK, 0 rows affected (0.039 sec)

MariaDB [(none)]> show databases;　　　　　　　　　　　　//查看数据库
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student_info       |
+--------------------+
4 rows in set (0.001 sec)

MariaDB [(none)]> use student_info;　　　　　　　　　　　　//应用数据库
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

三、数据表的基本操作

MariaDB [student_info]> show tables;　　　　　　　　　　//查看数据库中的表们
+------------------------+
| Tables_in_student_info |
+------------------------+
| stu_info               |
+------------------------+
1 row in set (0.001 sec)

MariaDB [student_info]> create table books(book_id INT, title TEXT, status INT);　　//创建表books
Query OK, 0 rows affected (0.186 sec)

MariaDB [student_info]> show tables;　　　　　　　　　　//查看数据库中的表们
+------------------------+
| Tables_in_student_info |
+------------------------+
| books                  |
| stu_info               |
+------------------------+
2 rows in set (0.001 sec)

MariaDB [student_info]> describe books;　　　　　　　　//查看表的详细结构
+---------+---------+------+-----+---------+-------+
| Field   | Type    | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+-------+
| book_id | int(11) | YES  |     | NULL    |       |
| title   | text    | YES  |     | NULL    |       |
| status  | int(11) | YES  |     | NULL    |       |
+---------+---------+------+-----+---------+-------+
3 rows in set (0.001 sec)

MariaDB [student_info]> insert into books values(100, 'Heart of Darkness', 0);　　　　//插入一条数据
Query OK, 1 row affected (0.066 sec)

MariaDB [student_info]> insert into books values(101, 'The Catcher of the Rye', 1);　　//插入第二条数据
Query OK, 1 row affected (0.033 sec)

MariaDB [student_info]> insert into books values(102, 'My Antonia', 0);　　　　　　　　//插入第三条数据
Query OK, 1 row affected (0.025 sec)

MariaDB [student_info]> insert into books values(103, 'Uncle's Home', 2);　　　　　　//插入第三条数据
Query OK, 1 row affected (0.033 sec)

MariaDB [student_info]> select * from books;　　　　　　　　　　　　　　　　　　　　　　　　//查询表的内容
+---------+------------------------+--------+
| book_id | title                  | status |
+---------+------------------------+--------+
|     100 | Heart of Darkness      |      0 |
|     101 | The Catcher of the Rye |      1 |
|     102 | My Antonia             |      0 |
|     103 | Uncle's Home           |      2 |
+---------+------------------------+--------+
4 rows in set (0.000 sec)

MariaDB [student_info]> select * from books where status = 0;　　　　　　　　　　　　　　//条件查询表的内容
+---------+-------------------+--------+
| book_id | title             | status |
+---------+-------------------+--------+
|     100 | Heart of Darkness |      0 |
|     102 | My Antonia        |      0 |
+---------+-------------------+--------+
2 rows in set (0.025 sec)

MariaDB [student_info]> select * from books where status = 0G;　　　　　　　　　　　　//查询表，改变显示方式
*************************** 1. row ***************************
book_id: 100
  title: Heart of Darkness
 status: 0
*************************** 2. row ***************************
book_id: 102
  title: My Antonia
 status: 0
2 rows in set (0.001 sec)

ERROR: No query specified

MariaDB [student_info]> update books set status = 1 where book_id = 102;　　　　　　//更新表信息
Query OK, 1 row affected (0.029 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [student_info]> select * from books where status = 1;　　　　　　　　　　　　//条件查询表的内容
+---------+------------------------+--------+
| book_id | title                  | status |
+---------+------------------------+--------+
|     101 | The Catcher of the Rye |      1 |
|     102 | My Antonia             |      1 |
+---------+------------------------+--------+
2 rows in set (0.001 sec)

MariaDB [student_info]> update books set status = 0 where book_id = 101;　　　　　　//更新表信息
Query OK, 1 row affected (0.022 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [student_info]> select * from books where status = 0;　　　　　　　　　　　　//条件查询表的内容
+---------+------------------------+--------+
| book_id | title                  | status |
+---------+------------------------+--------+
|     100 | Heart of Darkness      |      0 |
|     101 | The Catcher of the Rye |      0 |
+---------+------------------------+--------+
2 rows in set (0.000 sec)

MariaDB [student_info]> update books set title = 'The Catcher in the Rye', status = 1 where book_id = 101;　　　　//更新表信息
Query OK, 1 row affected (0.030 sec)
Rows matched: 1  Changed: 1  Warnings: 0

四、表的高级操作

MariaDB [student_info]> create table status_names(status_id INT, status_name char(8));　　　　　　//创建表
Query OK, 0 rows affected (0.182 sec)

MariaDB [student_info]> insert into status_names values(0, 'inactive'), (1, 'active'), (2, 'inactive');　　//向表中插入数据
Query OK, 3 rows affected (0.038 sec)
Records: 3  Duplicates: 0  Warnings: 0

MariaDB [student_info]> select * from status_names;　　　　//查询表内容
+-----------+-------------+
| status_id | status_name |
+-----------+-------------+
|         0 | inactive    |
|         1 | active      |
|         2 | inactive    |
+-----------+-------------+
3 rows in set (0.000 sec)

MariaDB [student_info]> select book_id, title, status_name from books join status_names where status = status_id;　　　　//两个表的链接操作
+---------+------------------------+-------------+
| book_id | title                  | status_name |
+---------+------------------------+-------------+
|     100 | Heart of Darkness      | inactive    |
|     101 | The Catcher in the Rye | active      |
|     102 | My Antonia             | active      |
|     103 | Uncle's Home           | inactive    |
+---------+------------------------+-------------+
4 rows in set (0.001 sec)

说明：

　　1、select book_id, title, status_name from books　　　　　　//从books表中选择特定的列们

　　2、join status_names　　　　　　　　　　　　　　　　　　//指定第二个表

　　3、where status = status_id　　　　　　　　　　　　　　　//指定查询条件

　　SELECT - 从数据库表中获取数据  

　　UPDATE - 更新数据库表中的数据  

　　DELETE - 从数据库表中删除数据   

　　INSERT INTO - 向数据库表中插入数据   

　　CREATE DATABASE - 创建新数据库   

　　ALTER DATABASE - 修改数据库   

　　CREATE TABLE - 创建新表   

　　ALTER TABLE - 变更（改变）数据库表   

　　DROP TABLE - 删除表   

　　CREATE INDEX - 创建索引（搜索键）   

　　DROP INDEX - 删除索引