MariaDB数据库基本操作

1、CMD打开执行命令：mysql -u root -p
    输入数据库密码，进入数据库

PS C:Usersadmin> mysql -u root -p
Enter password: ****
Welcome to the MariaDB monitor.  Commands end with ; or g.
Your MariaDB connection id is 11
Server version: 10.4.7-MariaDB mariadb.org binary distribution

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

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

2、执行show databases; ,查看MariaDB的数据库结构。

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| django             |
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.000 sec)

3、新建一个库，名字叫my。

MariaDB [test]> create database my;
Database changed

4、可以再次通过show databases查看新建的库

5、使用库：use my

6、新建一个表单：sql语句如下
    

    MariaDB [my]> create table my.student(
    -> id int(4) primary key,
    -> name varchar(4) not null,
    -> age int(2) not null
    -> );

  注：语句的结构如果错误，就会出现问题。错一点点都不行，反例如下：

MariaDB [my]> create table my.student(
    -> id int(4) primary key,
    -> name varchar(4) not null,
    -> age int(2) not null,               #此处多了一个,导致了报错
    -> );
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ')' at line 5

7、查看表情况

MariaDB [my]> show tables;
+--------------+
| Tables_in_my |
+--------------+
| student      |
+--------------+
1 row in set (0.000 sec)

8、查看表的字段信息

MariaDB [my]> desc student
    -> ;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| id    | int(4)     | NO   | PRI | NULL    |       |
| name  | varchar(4) | NO   |     | NULL    |       |
| age   | int(2)     | NO   |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
3 rows in set (0.011 sec)

注：CMD内执行命令，如果结束了必须得带上分号 ;



9、 改变表的结构
eg1 新增字段address

MariaDB [my]> alter table student add address varchar(48);
Query OK, 0 rows affected (0.007 sec)
Records: 0  Duplicates: 0  Warnings: 0

eg2 新增字段gender

MariaDB [my]> alter table student add gender enum("boy","girl") after age;
Query OK, 0 rows affected (0.008 sec)
Records: 0  Duplicates: 0  Warnings: 0

语句必须要正确，不然一定会报错。如下：

MariaDB [my]> alert table student add address varchar(48);
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'alert table student add address varchar(48)' at line 1

这里的错误是语句alter，这里打成了alert


10、表结构改变成功后查看结构

MariaDB [my]> desc student;

+---------+--------------------+------+-----+---------+-------+
| Field   | Type               | Null | Key | Default | Extra |
+---------+--------------------+------+-----+---------+-------+
| id      | int(4)             | NO   | PRI | NULL    |       |
| name    | varchar(4)         | NO   |     | NULL    |       |
| age     | int(2)             | NO   |     | NULL    |       |
| gender  | enum('boy','girl') | YES  |     | NULL    |       |
| address | varchar(48)        | YES  |     | NULL    |       |
+---------+--------------------+------+-----+---------+-------+
5 rows in set (0.007 sec)

11、修改表字段
eg1 将gender修改为sex

MariaDB [my]> alter table student change gender sex enum("boy","girl") not null;

Query OK, 0 rows affected (0.014 sec)
Records: 0  Duplicates: 0  Warnings: 0

查看表结构信息

MariaDB [my]> desc student;
+---------+--------------------+------+-----+---------+-------+
| Field   | Type               | Null | Key | Default | Extra |
+---------+--------------------+------+-----+---------+-------+
| id      | int(4)             | NO   | PRI | NULL    |       |
| name    | varchar(4)         | NO   |     | NULL    |       |
| age     | int(2)             | NO   |     | NULL    |       |
| sex     | enum('boy','girl') | NO   |     | NULL    |       |
| address | varchar(48)        | YES  |     | NULL    |       |
+---------+--------------------+------+-----+---------+-------+
5 rows in set (0.007 sec)