一、SQL语句
分类：
- DDL: Data Defination Language 数据定义语言
CREATE，DROP，ALTER - DML: Data Manipulation Language 数据操纵语言
INSERT，DELETE，UPDATE - DCL：Data Control Language 数据控制语言
GRANT，REVOKE，COMMIT，ROLLBACK - DQL：Data Query Language 数据查询语言
SELECT
1.1 数据查询语言
语法：
SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]
字段显示可以使用别名：
col1 AS alias1, col2 AS alias2, ...WHERE子句：指明过滤条件以实现“选择”的功能：
过滤条件：布尔型表达式
算术操作符：+, -, *, /, %
比较操作符：=,<=>（相等或都为空）, <>, !=(非标准SQL), >, >=, <, <=
BETWEEN min_num AND max_num
IN (element1, element2, ...)
IS NULL
IS NOT NULL
GROUP：根据指定的条件把查询结果进行“分组”以用于做“聚合”运算
avg(), max(), min(), count(), sum()
HAVING: 对分组聚合运算后的结果指定过滤条件ORDER BY: 根据指定的字段对查询结果进行排序
升序：ASC
降序：DESCLIMIT [[offset,]row_count]：对查询的结果进行输出行数数量限制
对查询结果中的数据请求施加“锁”
FOR UPDATE: 写锁，独占或排它锁，只有一个读和写
LOCK IN SHARE MODE: 读锁，共享锁，同时多个读
1.2 常用DQL语句
导入hellodb_innodb.sql生成数据库，用于测试
[root@localhost ~]# mysql -uroot -p
Enter password:
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 27
Server version: 10.2.25-MariaDB-log Source 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.
MariaDB [(none)]> source hellodb_innodb.sql;
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 1 row affected (0.00 sec)
Database changed
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 8 rows affected (0.00 sec)
Records: 8 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.04 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 14 rows affected (0.00 sec)
Records: 14 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 7 rows affected (0.00 sec)
Records: 7 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 15 rows affected (0.00 sec)
Records: 15 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 25 rows affected (0.01 sec)
Records: 25 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.03 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
MariaDB [hellodb]> show databases;
+--------------------+
| Database |
+--------------------+
| db |
| db1 |
| hellodb |
| information_schema |
| mysql |
| performance_schema |
+--------------------+
6 rows in set (0.00 sec)
MariaDB [hellodb]> use hellodb;show tables;
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes |
| coc |
| courses |
| scores |
| students |
| teachers |
| toc |
+-------------------+
7 rows in set (0.00 sec)
示例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]> 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)
示例2：以ClassID为分组依据，显示每组的平均年龄
MariaDB [hellodb]> select classid,avg(age) as '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)
示例3：显示第2题中平均年龄大于30的分组及平均年龄
MariaDB [hellodb]> select classid,avg(age) as '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)
示例4：显示以L开头的名字的同学的信息
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)
二、MySQL用户和权限管理
管理类：
CREATE TEMPORARY TABLES
CREATE USER
FILE
SUPER
SHOW DATABASES
RELOAD
SHUTDOWN
REPLICATION SLAVE
REPLICATION CLIENT
LOCK TABLES
PROCESS程序类： FUNCTION、PROCEDURE、TRIGGER
CREATE
ALTER
DROP
EXCUTE库和表级别：DATABASE、TABLE
ALTER
CREATE
CREATE VIEW
DROP
INDEX
SHOW VIEW
GRANT OPTION：能将自己获得的权限转赠给其他用户
权限对象：
- 数据操作
SELECT
INSERT
DELETE
UPDATE - 字段级别
SELECT(col1,col2,...)
UPDATE(col1,col2,...)
INSERT(col1,col2,...) - 所有权限
ALL PRIVILEGES 或 ALL
授权语法：
GRANT priv_type [(column_list)],... ON [object_type] priv_level TO 'user'@'host' [IDENTIFIED BY 'password'] [WITH GRANT OPTION];
- priv_type: ALL [PRIVILEGES]
- object_type:TABLE | FUNCTION | PROCEDURE
- priv_level: (所有库) | . | db_name. | db_name.tbl_name | tbl_name(当前库的表) | db_name.routine_name(指定库的函数,存储过程,触发器)
- with_option: GRANT OPTION
| MAX_QUERIES_PER_HOUR count
| MAX_UPDATES_PER_HOUR count
| MAX_CONNECTIONS_PER_HOUR count
| MAX_USER_CONNECTIONS count
示例：授权magedu用户，允许192.168.1.0/24网段可以连接mysql
MariaDB [hellodb]>
GRANT USAGE ON *.* TO 'magedu'@'192.168.1.%' IDENTIFIED BY '000000';
MariaDB [hellodb]> SHOW GRANTS FOR 'magedu'@'192.168.1.%';
+-----------------------------------------------------------------------------------------------------------------+
| Grants for [email protected].% |
+-----------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'magedu'@'192.168.1.%' IDENTIFIED BY PASSWORD '*032197AE5731D4664921A6CCAC7CFCE6A0698693' |
+-----------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
三、Mysql常见存储引擎以及特点
常见存储引擎：MyISAM、Innodb
MyISAM引擎特点
- 不支持事务
- 表级锁定
- 读写相互阻塞，写入不能读，读时不能写
- 只缓存索引
- 不支持外键约束
- 不支持聚簇索引
- 读取数据较快，占用资源较少
- 不支持MVCC（多版本并发控制机制）高并发
- 崩溃恢复性较差
- MySQL5.5.5前默认的数据库引擎
MyISAM存储引擎适用场景：
只读（或者写较少）、表较小（可以接受长时间进行修复操作）
- MyISAM引擎文件
tbl_name.frm 表格式定义
tbl_name.MYD 数据文件
tbl_name.MYI 索引文件
InnoDB引擎特点
行级锁
支持事务，适合处理大量短期事务
读写阻塞与事务隔离级别相关
可缓存数据和索引
支持聚簇索引
崩溃恢复性更好
支持MVCC高并发
从MySQL5.5后支持全文索引
从MySQL5.5.5开始为默认的数据库引擎
InnoDB引擎文件
所有InnoDB表的数据和索引放置于同一个表空间中
表空间文件：datadir定义的目录下
数据文件：ibddata1, ibddata2, ...
每个表单独使用一个表空间存储表的数据和索引
启用：innodb_file_per_table=ON
默认ON (>= MariaDB 5.5)
两类文件放在数据库独立目录中
数据文件(存储数据和索引)：tb_name.ibd
表格式定义：tb_name.frm