[MySQL beginner series five]: Introduction to advanced features of MySQL and introduction to MySQL security

We have already briefly talked about the installation of mysql and other introductions, and the "add, delete and modify" operations in MySQL.

As an industry-leading database management system, MySQL has many advanced features. This article will focus on indexes, views, stored procedures, triggers and transaction processing in MySQL.

[MySQL Beginner Series 1]: Teach you how to get started with MySQL

[MySQL Beginner Series 2]: Teach you how to get started with MySQL - database and data table operations

[MySQL Beginner Series 3]: Add, delete and modify operations of MySQL

[MySQL Beginner Series 4]: Teach you how to query MySQL data from beginner to apprentice

Let everyone have a concept first, which is convenient for learning, and we will write advanced articles later.

1. Introduction to database indexes and how to use indexes to speed up queries

An index is a data structure used to speed up database queries. Its basic principle is to avoid full table scans during queries and use binary search to quickly locate data during queries. MySQL supports various types of indexes, including simple indexes, primary key indexes, unique indexes, and full-text indexes. The use of indexes can greatly improve the efficiency of data query, but the maintenance and use of indexes also require a certain cost.
The commonly used index types in MySQL are as follows:

Simple index: refers to the ordinary index created on a column. Can speed up queries, but does not guarantee unique values in the column.
Primary key index: An index sorted based on one or more columns, used to uniquely identify a record.
Unique Index: Similar to primary key, but can contain null values.
Full-text index: used for full-text search, often used for columns of text data type.
B-tree index: An index implemented based on the B-tree data structure, suitable for equivalence queries and range queries.
B+ tree index: an index based on the B+ tree data structure, suitable for equivalence query and range query.
Hash index: An index based on a hash table, suitable for equivalent queries.
Spatial index: An index suitable for spatial data, which can quickly locate the location of spatial objects.

While using indexes, you also need to pay attention to the following issues:

Index selection: You should select the appropriate index type according to the actual situation of the query, and do not add indexes blindly.
Number of indexes: Excessive indexes will increase space and maintenance costs, and should be added carefully according to the actual situation.
Index update: insert, update and delete operations will affect the update of the index, and frequent update operations should be avoided.
Composite index: Combining indexes of multiple columns can improve query efficiency, but you need to pay attention to the sorting method and order of the indexes.
Indexes can improve query efficiency, but they take up disk space and affect data insertion and update operations, because each time data is inserted and updated, the index needs to be updated accordingly.
The creation of indexes needs to be weighed and selected according to the specific situation. If the amount of data in the table is large, or frequent insert and update operations are required, creating too many indexes may affect performance.
When using an index, you need to pay attention to the selection and use of the index to avoid excessive indexing, and you also need to pay attention to avoid using too many joint indexes, because the joint index needs to meet certain conditions to take effect.

Second, the role of the view and how to create a view

A view is a virtual table that can integrate data from multiple tables, and a part of the data can be obtained through view queries. View separates the logical structure and physical structure of table data, which is a very important data abstraction technology. Views play a big role in multi-table queries, data separation, and access control.

Simplify complex queries: Through views, query results from multiple tables can be combined into one table, thereby simplifying complex query operations.
Protect data privacy: Views can hide part of the data and only show users the data they need to see to protect data privacy.
Improve query performance: Views can cache query results to avoid multiple executions of the same query operation and improve query performance.

In MySQL, the syntax for creating a view is as follows:

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

Among them, view_name represents the name of the new view,
column1, column2, etc. represent the column name or expression to be queried,
table_name represents the name of the table to be queried, and
the WHERE condition represents the data filter condition.

For example, the following statement creates a view called "employee_info" that displays employee names, salaries, and department names:

CREATE VIEW employee_info AS  
SELECT employees.name, employees.salary, departments.department_name  
FROM employees  
JOIN departments ON employees.department_id = departments.department_id;

After creating a view, you can use the view name to query the view using the SELECT statement, for example:

SELECT * FROM employee_info;

This will return all the data in the view "employee_info".

3. The use and examples of stored procedures and triggers

3.1 Stored procedure

Stored Procedure (Stored Procedure) is a set of pre-written collections to complete specific tasks, stored in the database, and invoked for execution through a keyword. A stored procedure can contain a series of SQL statements that can be created, deleted, modified, or invoked in the database.

A trigger (Trigger) is a special stored procedure that is automatically triggered when a table in the database performs a specific operation (such as insert, update, or delete). Triggers can be used to enforce data integrity constraints, or to perform actions when data changes.
Here's an example of creating a stored procedure that adds two numbers and returns the result:

CREATE PROCEDURE AddNumbers  
   @FirstNumber INT,  
   @SecondNumber INT,  
   @Result INT OUTPUT  
AS  
BEGIN  
   SET @Result = @FirstNumber + @SecondNumber  
   RETURN @Result  
END

In the above example, we created a stored procedure named AddNumbers that takes two integer parameters and returns the sum of these two numbers. The @Result parameter in the stored procedure is an output parameter used to return the calculation result.
Here is an example of calling a stored procedure:

EXEC AddNumbers 5, 10, @Result OUTPUT  
SELECT @Result

In the above example, we called the AddNumbers stored procedure through the EXECUTE statement and passed 5 and 10 as input parameters to it. The result returned by the stored procedure is stored in the @Result variable and output through the SELECT statement.
Here's an example of creating a trigger that will save the insertion timestamp in another table every time a new record is inserted:

CREATE TRIGGER InsertTimestampTrigger  
ON InsertedTable  
FOR INSERT  
AS  
BEGIN  
   INSERT INTO TimestampTable (Timestamp)  
   SELECT GETDATE()  
END

In the above example, we have created a trigger called InsertTimestampTrigger which will fire when a new record is inserted in the InsertedTable table. The trigger saves the current timestamp into another table, TimestampTable.
The trigger will be executed automatically when we insert a new record in the InsertedTable table:

INSERT INTO InsertedTable (Name, Value) VALUES ('Test', 123)

In the above example, we insert a new record into the InsertedTable table, which will trigger the InsertTimestampTrigger trigger and save the current timestamp in the TimestampTable table.

Fourth, learn the concept of transactions, ACID properties, and how to ensure data consistency

4.1 Transaction

Transaction (Transaction) refers to a set of database operations that either all execute successfully or fail and roll back. A transaction is an atomic operation that either executes successfully or fails and rolls back.

4.2 ACID

ACID refers to the four basic characteristics that database transactions need to meet for correct execution:

Atomicity: All operations in a transaction are either executed successfully, or all failed and rolled back.
Consistency: After the transaction is executed, the data in the database must meet the consistency constraints of the database.
Isolation: Concurrently executed transactions do not interfere with each other, and transactions are executed independently without affecting each other.
Durability: After the transaction is successfully executed, the modification to the data is permanently saved in the database and will not be lost even if a system failure occurs.

4.3 Data Consistency

Data consistency refers to the consistency of data in the database among multiple copies. In a distributed database system, data is distributed on different nodes, and each node has its own copy, so it is necessary to ensure the data consistency between these copies.
There are three types of data consistency:

Strong consistency: When data is updated, all replicas will see the updated data immediately.
Weak consistency: When data is updated, all replicas will eventually see the updated data, but not necessarily immediately.
Final consistency: When data is updated, all replicas will eventually see the updated data, but for a period of time, there may be data inconsistencies.

In order to achieve data consistency, distributed database systems usually use technologies such as data replication and data synchronization to ensure data consistency among multiple copies. At the same time, it is also necessary to consider how to deal with node failures, network interruptions and other issues to ensure the reliability and availability of the database.

In order to ensure data consistency, the following measures are usually required:

Use transactions: Encapsulate data operations in transactions to ensure atomicity, consistency, and isolation of operations.
Reasonable design of transaction concurrency strategy: According to business requirements and characteristics of data operations, select an appropriate concurrency strategy, such as read-write lock, row lock, table lock, etc.
Avoid concurrency conflicts: reduce the possibility of concurrency conflicts through reasonable design and optimization, such as using partition tables, sub-databases and sub-tables and other technologies.
Implement data backup and recovery strategies: Regularly perform data backup to ensure that data will not be lost due to system failure, and can restore data to the latest state after a failure occurs.
Use a reliable network transmission protocol: When performing distributed system data transmission, use a reliable network transmission protocol to ensure data integrity and consistency.
Monitoring and logging: monitor and log database and data operations, discover and deal with problems in a timely manner, and ensure data consistency and reliability.

5. Introduction to MySQL security related concepts

5.1 MySQL security settings

MySQL security settings include the following aspects:

User rights management: MySQL supports multi-user management and can assign different rights to different users. Different access permissions can be set for each user, such as read-only, read-write, full control, etc.
Database encryption: MySQL supports the encryption of the database, which can use AES, DES and other algorithms to encrypt the database to protect the security of the data.
Network security: MySQL can restrict database access by configuring a network access control list (ACL), allowing only trusted source IP addresses to access the database.
Database backup: MySQL’s backup operation can back up data locally or remotely, and regularly back up data to ensure that data will not be lost due to attacks, failures, and other reasons.
Logging: MySQL supports recording operation logs, which can record user logins, operations, and other behaviors for security auditing and tracking.

5.2 Database maintenance operation methods, including backup and recovery of data in MySQL

There are several ways to back up MySQL data:

Backup using the mysqldump command: use the command line tool, enter "mysqldump -u username -p dbname tablename > filename.sql" to back up the SQL statement of the specified table in the specified database.
Backup using MySQL Workbench: MySQL Workbench is a graphical tool officially launched by MySQL, through which you can perform database backup.
Use third-party backup tools: such as Xtrabackup, mysqldbcopy, etc.
There are several ways to restore MySQL data:
Restoring using the mysql command: using the command line tool, enter "mysql -u username -p dbname < filename.sql" to restore the backup SQL statement.
Recovery using MySQL Workbench: Database recovery can be performed through MySQL Workbench.
Use third-party recovery tools: such as Xtrabackup, mysqldbcopy, etc.
It should be noted that when performing database backup and recovery, an appropriate time point and method should be selected to avoid affecting the normal operation of the database and data consistency. Moreover, during the backup and restoration process, attention should be paid to the security of backup files and restored files to avoid data loss or leakage.

5.3 SQL Injection

SQL injection means that attackers use vulnerabilities in web applications to send malicious SQL query statements to the background database server to obtain or tamper with sensitive information in the database, or to achieve unauthorized operations. Attackers usually implement SQL injection attacks by inserting specific SQL codes into web forms or inserting malicious codes into URL parameters.
For example, an attacker can enter a string similar to "admin' OR 1=1 --" in a web form, which will cause the background database to execute unwanted SQL queries, thereby leaking sensitive information or performing other malicious operations.
To avoid SQL injection attacks, developers can take the following precautions:

Use parameterized queries: pass the data entered by the user to the database server as query parameters instead of splicing it into the SQL query statement.
Filter and verify the input data: Strictly filter and verify the data entered by the user to ensure that only the expected data type and format can pass the verification.
Restrict database privileges: Only grant necessary database privileges to applications to avoid security problems caused by over-authorization.
Use secure programming frameworks: Use secure programming frameworks and tools to write web applications, such as Spring Security, OWASP ESAPI, etc.
Logging: Record all user operations and database queries for security auditing and tracking.

There are many security issues with MySQL, and various measures need to be taken to improve its security, timely updating and patching.