MariaDB表查询以及用户管理实践
Posted 1874
tags:
篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了MariaDB表查询以及用户管理实践相关的知识，希望对你有一定的参考价值。
从1、 导入hellodb.sql生成数据库
[root@test-centos7-node1 ~]# rz rz waiting to receive. zmodem trl+C ȡ 100% 7 KB 7 KB/s 00:00:01 0 Errors Transferring hellodb_innodb.sql... [root@test-centos7-node1 ~]# ls hellodb_innodb.sql [root@test-centos7-node1 ~]# mysql < hellodb_innodb.sql [root@test-centos7-node1 ~]# mysql Welcome to the MariaDB monitor. Commands end with ; or \\g. Your MariaDB connection id is 4 Server version: 5.5.64-MariaDB MariaDB Server 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)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | hellodb | | mysql | | performance_schema | | test | +--------------------+ 5 rows in set (0.00 sec) MariaDB [(none)]> use hellodb 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 MariaDB [hellodb]> show tables; +-------------------+ | Tables_in_hellodb | +-------------------+ | classes | | coc | | courses | | scores | | students | | teachers | | toc | +-------------------+ 7 rows in set (0.00 sec) MariaDB [hellodb]>
说明：导入数据库，可以用输入重定向到方式，如上所示，也可以在数据库里用source sql脚本路径的方式导入，两种的方式核心思想就是把sql脚本交给mysql数据库引擎执行一遍，生成数据。
(1) 在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄
MariaDB [hellodb]> show tables; +-------------------+ | Tables_in_hellodb | +-------------------+ | classes | | coc | | courses | | scores | | students | | teachers | | toc | +-------------------+ 7 rows in set (0.00 sec) MariaDB [hellodb]> desc students; +-----------+---------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+---------------------+------+-----+---------+----------------+ | StuID | int(10) unsigned | NO | PRI | NULL | auto_increment | | Name | varchar(50) | NO | | NULL | | | Age | tinyint(3) unsigned | NO | | NULL | | | Gender | enum(\'F\',\'M\') | NO | | NULL | | | ClassID | tinyint(3) unsigned | YES | | NULL | | | TeacherID | int(10) unsigned | YES | | NULL | | +-----------+---------------------+------+-----+---------+----------------+ 6 rows in set (0.00 sec) MariaDB [hellodb]> select name,age from students where age > 25 and gender=\'M\'; +--------------+-----+ | name | age | +--------------+-----+ | Xie Yanke | 53 | | Ding Dian | 32 | | Yu Yutong | 26 | | Shi Qing | 46 | | Tian Boguang | 33 | | Xu Xian | 27 | | Sun Dasheng | 100 | +--------------+-----+ 7 rows in set (0.00 sec) MariaDB [hellodb]>
(2) 以ClassID为分组依据，显示每组的平均年龄
MariaDB [hellodb]> select * from students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [hellodb]> select classid , avg(age) from students group by classid; +---------+----------+ | classid | avg(age) | +---------+----------+ | NULL | 63.5000 | | 1 | 20.5000 | | 2 | 36.0000 | | 3 | 20.2500 | | 4 | 24.7500 | | 5 | 46.0000 | | 6 | 20.7500 | | 7 | 19.6667 | +---------+----------+ 8 rows in set (0.00 sec) MariaDB [hellodb]>
(3) 显示第2题中平均年龄大于30的分组及平均年龄
ariaDB [hellodb]> select classid , avg(age) from students group by classid; +---------+----------+ | classid | avg(age) | +---------+----------+ | NULL | 63.5000 | | 1 | 20.5000 | | 2 | 36.0000 | | 3 | 20.2500 | | 4 | 24.7500 | | 5 | 46.0000 | | 6 | 20.7500 | | 7 | 19.6667 | +---------+----------+ 8 rows in set (0.00 sec) MariaDB [hellodb]> select classid , avg(age) from students group by classid having avg(age) > 30; +---------+----------+ | classid | avg(age) | +---------+----------+ | NULL | 63.5000 | | 2 | 36.0000 | | 5 | 46.0000 | +---------+----------+ 3 rows in set (0.00 sec) MariaDB [hellodb]>
(4) 显示以L开头的名字的同学的信息
MariaDB [hellodb]> select * from students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [hellodb]> select * from students where name like \'L%\'; +-------+-------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+-------------+-----+--------+---------+-----------+ | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | +-------+-------------+-----+--------+---------+-----------+ 3 rows in set (0.00 sec) MariaDB [hellodb]>
2、数据库授权magedu用户，允许192.168.1.0/24网段可以连接mysql
MariaDB [hellodb]> select user,host,password from mysql.user; +------+--------------------+----------+ | user | host | password | +------+--------------------+----------+ | root | localhost | | | root | test-centos7-node1 | | | root | 127.0.0.1 | | | root | ::1 | | | | localhost | | | | test-centos7-node1 | | +------+--------------------+----------+ 6 rows in set (0.00 sec) MariaDB [hellodb]> grant all on *.* to magedu@\'192.168.1.%\' identified by \'admin\'; Query OK, 0 rows affected (0.01 sec) MariaDB [hellodb]> select user,host,password from mysql.user; +--------+--------------------+-------------------------------------------+ | user | host | password | +--------+--------------------+-------------------------------------------+ | root | localhost | | | root | test-centos7-node1 | | | root | 127.0.0.1 | | | root | ::1 | | | | localhost | | | | test-centos7-node1 | | | magedu | 192.168.1.% | *4ACFE3202A5FF5CF467898FC58AAB1D615029441 | +--------+--------------------+-------------------------------------------+ 7 rows in set (0.00 sec) MariaDB [hellodb]>
说明：此方式是创建用户+授权一起做，当然也可以用先创建账号，然后在授权，有关mysql的账号创建和授权可以参考https://www.cnblogs.com/qiuhom-1874/p/9741166.html
3、总结mysql常见的存储引擎以及特点。
MyISAM引擎特点：
1）不支持事务
2）支持表级别锁定
3）读写相互阻塞，写入不能读，读时不能写
4）只缓存索引
5）不支持外键约束
6）不支持聚簇索引
7）读取数据较快，占用资源较少
8）不支持MVCC（多版本并发控制机制）高并发
9）崩溃恢复性较差
10）mysql5.5前默认的数据库引擎
MyISAM存储引擎适用于只读（或者写较少）、表较小（可以接受长时间进行修复操作）的场景
MyISAM引擎文件有三个.frm（表格式定义文件） .MYD（数据文件） .MYI（索引文件）
InnoDB引擎特点：
1）支持事务，适合处理大量短期事务
2）支持行级别锁
3）读写阻塞与事务隔离级别相关
4）可缓存数据和索引
5）支持聚簇索引
6）崩溃恢复性更好
7）支持MVCC高并发
8）从mysql5.5后支持全文索引，mysql5.5开始默认的数据库引擎，InnoDB数据库文件所有InnoDB表达数据和索引放置于同一个表空间中，表空间文件是由主配置文件中的datadir来指定存放的位置，数据文件：ibddata1,idbdata2……，若每个表单独使用一个表空间存储表的数据和索引，可在主配置文件中用innodb_file_per_table=ON来启用，两类文件放在数据库独立目录中，其中数据文件（存储数据和索引）是以标名加.ibd结尾的文件，表格式文件是表名加.frm结尾的文件
以上是关于MariaDB表查询以及用户管理实践的主要内容，如果未能解决你的问题，请参考以下文章