1. Basic introduction to databases
A database is a structured organizational system, consisting of a collection of data that is organized and stored to provide the ability to access, update and process data in an organized manner. and efficiency. Databases play an important role in information management, providing a basic platform for applications and users to retrieve information according to specific needs. The main goal of a database is to provide a means to organize data so that it can be easily retrieved and processed. This is typically done through the use of data structures such as tables, relationships, and rules to ensure integrity, safety, and performance in data management.
Databases are capable of storing and managing different types of data, from text data to complex multimedia data. It provides methods to query, update and process data, as well as ensure the consistency and uniformity of information during use. A special feature of databases is the ability to share data, allowing multiple users and applications to access data at the same time, with access control mechanisms to ensure data security and consistency. Whether.
2. Meaning and role of databases in information technology
Databases play an extremely important role in the field of information technology with the following main effects:
Data storage: Databases are important in storing and managing diverse forms of information from different sources. Containing information about customers, products, and financial data, databases provide a structured platform to organize, preserve, and access information easily and effectively. This aids in strategic decision-making, optimizes operations and customer interactions, and ensures the integrity and security of an organization’s critical data.
Information management: By organizing data according to a predefined structure, databases create a data storage environment that is easy to retrieve and process. Organizing information into appropriate tables, relationships, and data structures helps optimize the data search and query process. At the same time, providing a user interface for easy and organized interaction with information, helps reduce complexity and increase intuitiveness when working with data.
Application support: Databases play an extremely important role in supporting information applications such as customer management systems (CRM), warehouse management systems (ERP), web and mobile applications. dynamic. These applications strongly depend on databases to store and retrieve information. CRM systems rely on databases to manage customer information, while ERP uses databases to manage production, finances and overall business operations. Databases provide flexible and reliable data storage, helping web and mobile applications perform interactions and retrieve information quickly and efficiently.
Security and data management: Databases ensure the integrity and security of critical information through security measures such as user authentication, data encryption, and authorization management. Regular data backups and establishment of data recovery strategies are also performed to ensure data recovery after incidents. An activity logging system is also applied to monitor and detect suspicious activities on the database.
A database is not simply a place to store data but also an important center that supports application development, creation of information services, and management of important information of organizations and individuals. enterprise.

3. Type of database
3.1. Relational Database
Relational Database (RDBMS) is a data storage system organized in the form of tables that are related to each other through primary and foreign keys. This is the most popular type of database in the information technology world. In an RDBMS, data is organized into tables, each representing a different entity or object. Rows in a table represent specific data items, while columns represent attributes or fields of information. The relationships between tables are determined through primary keys and foreign keys. A primary key is a column or set of columns that uniquely identifies each row in a table, while a foreign key is a column or set of columns in one table that references a primary key in another table.

MySQL, PostgreSQL, Oracle are popular relational database management systems, each with special features and widely used in applications ranging from personal to business projects. big. SQL (Structured Query Language) is commonly used to query, add, modify, and delete data from relational databases. SQL provides statements such as SELECT, INSERT, UPDATE, DELETE to perform operations on data. Practical applications of relational databases are very diverse. For example, a store management system might use a relational database to store information about products, orders from customers, customer information, and inventory management. In the banking sector, relational databases are used to store information about bank accounts, transactions, and personal financial history.

3.2. Non-relational Database
Non-relational Database (NoSQL) is a data storage system that does not follow the traditional relational model. This is often the choice when you need to store data with complex structures, heterogeneous data, or need to expand flexibly. Unlike relational databases, NoSQL does not require a fixed schema and is often used for large-scale web applications or storing diverse data such as user data, sensor data, and database data. multimedia. In non-relational databases, data is often organized as key-value pairs, columns (column-family), documents (documents) or graphs (graphs), depending on the type of database. specifically. This allows for structured data storage that is flexible and can scale easily with the size of the application.

For example, MongoDB is a popular document database in NoSQL. It stores data as flexible JSON documents that do not require a fixed schema, which makes it easier to change the data structure. Cassandra, a column-family database, is suitable for efficiently storing and retrieving columnar data in systems with large data volumes. Redis, a key-value database, is often used for caching data or managing session data in web applications with high performance requirements.

The practical applications of non-relational databases are very diverse. For example, in social applications or social networks, where it is necessary to store user information, relationships between users, posts, images and videos, a non-relational database like MongoDB is very useful. In the field of IoT (Internet of Things), where large volumes of data from sensors need to be stored and processed quickly, Cassandra is often used. Each type of non-relational database has specific advantages and applications in different situations, meeting the diverse needs of modern applications.

3.3. Other types of databases (Graph Database, Document Store, etc.)
In addition to the two main types of databases above, there exist many other types of databases designed to address specific data storage and retrieval needs:

Graph Database: Used to store data with complex relationships, especially in social network systems, networks, or graph-structured data types. Neo4j is a popular graph database management system with the ability to handle complex relationships between objects.
Document Store: Stores data in the form of flexible structured documents such as JSON or XML. Suitable for applications that need non-permanent, flexible data storage. A practical example of a Document Store is Couchbase, which is widely used to store diverse data such as user information, support structure for heterogeneous data, and is easily scalable.
The actual application of these types of databases depends on the characteristics of the data and the specific requirements of the application. For example, in the field of network analysis science, Graph Database is used to analyze relationships between complex elements. In user interface applications, Document Store is applied to store flexible and heterogeneously structured user information. The choice between these types of databases is often based on their properties specific data and application needs.

4. SQL database query language (Structured Query Language)
Introduction to Structured Query Language (SQL)
Structured Query Language (SQL) is a programming language used to manage and interact with relational databases. Used to perform operations such as querying, updating, deleting, and adding data to a relational database. SQL allows users to execute statements to query data from the database to get the necessary information, as well as perform operations to update, delete or add new data into the database.
The language has a specific syntax, including statements such as SELECT (to query data), INSERT (to add new data), UPDATE (to update data), DELETE (to delete data), and Other database control statements such as CREATE, ALTER, DROP to manage the structure of the database. SQL is not only used in popular database management systems such as MySQL, PostgreSQL, SQL Server, Oracle but is also a widely applied standard language in the field of information technology and database management. database.

Basic SQL query commands

SQL is a standard language used to query and manage relational databases. Basic commands in SQL include:

CREATE: Used to create a new database, new table, or other objects in the database.
ALTER: Allows changing the structure of objects in the database such as adding columns, deleting columns, changing data types, etc.
DROP: Delete objects in the database such as tables, indexes, or the database itself.
SELECT: Used to retrieve data from the database.
INSERT: Add new data into the database.
UPDATE: Updates existing data in the database.
DELETE: Delete data from the database.
Query commands: SELECT, INSERT, UPDATE, DELETE

SELECT: This command is used to query data from the database. The basic syntax is SELECT * FROM table_name to get all the data from the table.
INSERT: This command is used to add new data into the database. For example: INSERT INTO table_name (column1, column2, …) VALUES (value1, value2, …).
UPDATE: Used to update existing data in the database. For example: UPDATE table_name SET column1 = value1 WHERE condition.
DELETE: Delete data from the database. The basic syntax is DELETE FROM table_name WHERE condition.
Advanced query requests: JOINs, Functions, Stored Procedures

JOINs: Used to combine data from multiple tables in the same query. JOIN types include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
Functions: SQL provides many built-in functions to perform operations on data such as mathematical functions, string functions, date functions, etc.
Stored Procedures: Is a block of SQL code stored in the database, which can be called and executed from applications. They help optimize and reuse SQL code.
Advanced commands and capabilities in SQL provide flexibility and power in querying, updating, and managing data in relational databases.

5. Database management
5.1. Backup and Restore data
Backing up and restoring data is an important process to ensure data safety and recovery in case something goes wrong.

Backup: The data backup process is an important part of database management, ensuring that the latest version of data is safely stored and can be restored when needed. This is typically done through the application of integrated backup tools or external solutions, with regular backup schedules such as daily or weekly. Backup data is often stored in various locations to ensure safety, and periodic audits and data recovery procedures are implemented to ensure data availability in the event of a disaster. problem. Storage diversification and regular backup testing both play important roles in maintaining data integrity and the ability to recover when needed.

Restore: The data recovery process (Restore) is the important process of returning data from backup copies when necessary due to data loss or failure. This ensures the possibility of reproducing the original data from the backups that have been created. Regularly checking and performing data recovery testing is important to ensure the process operates reliably, and can regenerate data as expected should the need arise. System administrators and database management teams need to establish and maintain a reliable Restore process, regularly testing and performing data recovery tests to ensure availability and capability. Recover data safely in necessary situations.

5.2. Database security
Database security is a critical element for protecting important information and preventing unauthorized access. Database security measures include:

Access management: Define and manage access to the database based on user roles and access levels. Database management systems (DBMS) often provide flexible access control mechanisms, allowing specific users, user groups, or roles to be defined to control access to data.
Data encryption: Use encryption to protect important information as it is stored or transmitted. By converting data into a format that is unreadable without a decryption key, encryption protects information from unauthorized access, even if the data is exposed.
Security check: Perform periodic security checks, audit logs to detect and prevent threatening activities. Systems log details of data access activities, database managers perform periodic audits to monitor for suspicious events, invalid access attempts or unauthorized data changes permission.
5.3. Performance management and optimization
Performance management: Ensure the database operates stably and efficiently. This includes monitoring and evaluating performance, fine-tuning the database structure, and handling load-related issues.
Query optimization: Use indexes, optimize queries, and perform other optimizations to improve database performance.
Upgrade and expand: Meet system growth needs by expanding the database in capacity, enhancing performance or implementing backup solutions.
Database management includes not only maintaining data integrity but also ensuring security and high performance during use and development.

6. Some real-life database applications
Use databases in different fields

Enterprise: Database is used in customer management system (CRM), ERP system management (Enterprise Resource Planning) to organize and manage information about products, customers, orders and finance.
Healthcare: In the healthcare field, databases are used to store patient records, test results, medication information, and other medical data. Medical management systems (EMR – Electronic Medical Records) rely on databases to provide accurate and easily accessible information.
Education: In education, databases are used to manage information about students, academic results, teaching schedules, and information related to the management of schools or training systems. create online.
Banking and Finance: Databases play an important role in managing customer information, financial transactions, asset data, and information related to risk and financial analysis. .
Some famous database systems

Oracle Database: One of the leading relational database systems widely used in large businesses and organizations.
MySQL: Popular open source relational database system used for small to mid-sized business and web applications.
MongoDB: This is one of the leading non-relational database systems, used to store flexible, non-permanent and diverse data in large-scale web applications.
Microsoft SQL Server: Microsoft’s relational database system is widely used in enterprise and information systems environments.
These database systems all play an important role in managing information, providing data for applications and ensuring the integrity and security of organizational and user data.