Database security refers to the collective measures and controls used to protect a database system from malicious attacks, unauthorized access, and any activities that could compromise the confidentiality, integrity, or availability of the database. It encompasses tools, policies, and procedures designed to secure the database environment.

The importance of database security cannot be overstated. A breach in database security can have devastating consequences, including:
1. Loss of Confidentiality: Unauthorized disclosure of sensitive or proprietary information. This could include customer personal identifiable information (PII), financial records, medical data (e.g., under regulations like HIPAA), trade secrets, or national security data.
2. Loss of Integrity: Unauthorized or accidental modification or destruction of data. This compromises the accuracy, consistency, and trustworthiness of the information, leading to incorrect reports, flawed business decisions, or operational failures.
3. Loss of Availability: Preventing legitimate users from accessing the database or specific data when needed (e.g., through a Denial-of-Service attack). This can halt business operations, lead to financial losses, and damage reputation.

Database systems face a multitude of threats from various sources, both internal and external:
- Unauthorized Access: The most prevalent threat, where individuals or systems gain access to data or functions they are not permitted to use. This can stem from weak authentication, stolen credentials, or unpatched vulnerabilities.
- Privilege Abuse: Legitimate users (employees, administrators) who misuse or exceed their authorized access privileges. This is an 'insider threat' and can be harder to detect.
- SQL Injection Attacks: A sophisticated attack technique that exploits vulnerabilities in application code to inject malicious SQL commands into the database, leading to unauthorized data access, modification, or deletion.

Access control is the fundamental process by which a DBMS regulates who can perform what operations on which data and database objects. It determines what an authenticated user or application is permitted to do once they have gained entry to the system.
- Authentication: The process of verifying a user's identity (e.g., username and password, biometric scan, digital certificate). This answers the question 'Who are you?'
- Authorization: The process of determining what an authenticated user is permitted to do. This answers the question 'What can you do?' Our focus in this section is on authorization.

Discretionary Access Control (DAC) is the most common and flexible type of access control model used in commercial database systems. In DAC, the owner of an object (e.g., the user who created a table or view) has the discretion (ability) to grant or revoke access privileges on that object to other users or groups. The 'discretionary' aspect comes from the fact that access rights are determined at the discretion of the object's owner.

Role-Based Access Control (RBAC) is an enhancement to DAC, specifically designed to simplify the management of privileges in large and complex database systems. Instead of directly granting privileges to individual users, privileges are grouped into roles, and then users are assigned to one or more roles. Users inherit all the privileges associated with the roles they are assigned.

SQL Injection (SQLi) is a particularly dangerous and common type of code injection attack that targets data-driven applications, especially web applications. It exploits vulnerabilities in an application's input validation and database query construction. An attacker inserts malicious SQL code into input fields (such as login forms, search bars, or URL parameters) that are then improperly handled by the application, leading to the database executing unintended commands.

How it Works (The Vulnerability):
The core vulnerability lies in applications that build SQL queries by directly concatenating user-supplied input strings without proper sanitization or parameterization.

Data encryption is the process of transforming data (called plaintext) into a coded or scrambled format (called ciphertext) to prevent unauthorized access. The transformation uses an encryption algorithm and an encryption key. Only those with the correct decryption key can convert the ciphertext back into its original, readable plaintext form.