DML(Data Manipulation Language)：INSERT， DELETE， UPDATE， SELECT
INSERT [INTO] tbl_name [(col1,...)] {VALUES|VALUE} (val1, ...),(...),...
假如有上面这张表
插入一行数据：insert students values(1,'xijinping',51,'zhonglanhai','m'); 字符串必须加引号，数字不能加引号
同时插入多行数据：insert students (id,name) values (2,'hujingtao'),(3,'jiangzeming');
SELECT：
查看一张表的全部字段：select * from students;
只查看指定的字段：select id,name from students;
将字段id取个别名：select id as stuid,name from students;
WHERE clause：用于指明挑选条件
col_name 操作符 value， 例如：age > 30
操作符(1) ：>, <, >=, <=, ==, !=
例如：select * from students where id=1;
select * from students where; 注意：后面的字符串要加引号，是否区分大小写，取决于字符类型，如果是
binary或者varbinary则区分大小写，char或者varchar则不需要区分大小写
组合条件：or,and,not
select name,age from students where age>=30 and age<=50;
select name,age from students where age between 30 and 50; 跟上面的语句是一个意思
操作符 ：BETWEEN ... AND ... LIKE 'PATTERN' RLIKE 'PATTERN'(正则表达式对字符串做模式匹配) IS NULL
IS NOT NULL
select name from students where name like '%ji%'; 注意像like，rlike这种查询方式性能极低
%：任意长度的任意字符 _：任意单个字符
select name from students where name rlike 'min$';
select name,age from students where age is null;
select id,name from students order by name; 根据name字段中的第一个字母排序，默认升序，加desc改为降序
注意其实执行DML语句首先都执行了select查询
DELETE：删除是相对应于行的
(1) DELETE FROM tbl_name WHERE where_condition
(2) DELETE FROM tbl_name [ORDER BY ...] [LIMIT row_count]
delete from students; (删除表的所有行）
delete from students where age is null;
小技巧：1. 快速创建相同结构的表，包括索引：MariaDB [test1]> create table a like students;
2.快速创建一个相同结构的表，但是不创建索引：MariaDB [test1]> create table b select * from students limit 0;
[root@localhost ~]# for i in {1..100}; do AGE=$[$RANDOM%100]; mysql -e "insert test1.a (id,name,age) values
($i,\"stu$i\",$AGE);"; done 为a这张表加入一些数据
delete from a order by age desc limit 20;
UPDATE：
update a set age=age-5 order by id desc limit 10;
update a set age=age-5 where name not like 'stu__';
用户账号及权限管理：
用户账号：'username'@'host'
禁止检查主机名：在my.cnf配置文件中的[mysqld]段添加skip_name_resolve = ON 一般都得添加此选项以提升性能
创建用户账号：CREATE USER 'username'@'host' [IDENTIFIED BY 'password'];
例如：create user 'testuser'@'192.168.%.%' identified by 'testpass'; 记得刷新用户授权表flush privileges;
删除用户账号：DROP USER 'user'@'host' [, user@host] ...
例如：drop user 'testuser'@'192.168.%.%';
查看用户授权表命令：select * from mysql.user\G;
授权：GRANT priv_type,... ON [object_type] db_name.tbl_name TO 'user'@'host' [IDENTIFIED BY 'password'];
例如：grant select,insert on test1.students to 'testuser'@'192.168.%.%';
查看指定用户所获得的授权：SHOW GRANTS FOR 'user'@'host'； SHOW GRANTS FOR CURRENT_USER;
回收权限：REVOKE priv_type, ... ON db_name.tbl_name FROM 'user'@'host';
例如：revoke insert on test1.students from 'testuser'@'192.168.%.%';
注意：MariaDB服务进程启动时，会读取mysql库的所有授权表至内存中
(1) GRANT或REVOKE命令等执行的权限操作会保存于表中，MariaDB此时一般会自动重读授权表，权限修改会立即生效
(2) 其它方式实现的权限修改，要想生效，必须手动运行FLUSH PRIVILEGES命令
mariadb安装完后密码是空的，这是不安全的，看下图;
可以使用该命令完成root密码设定：[root@localhost ~]# mysql_secure_installation