Role-based access control (RBAC) is a security measure that restricts system access based on a user's role within an organization. Testing RBAC ensures that only users with the appropriate roles are able to access specific resources or perform certain actions within the database. Verifying RBAC functionality helps maintain data confidentiality and prevent unauthorized access, enhancing overall security measures.

Regression testing verifies that changes made to the database haven't introduced new defects or impacted existing functionalities.

Reviewing the database change deployment logs should be the first step in troubleshooting as it provides insights into any errors or issues that occurred during the deployment process, helping identify the root cause more efficiently.

Stress testing assesses the system's ability to withstand extreme conditions such as high traffic volumes or heavy loads. By pushing the system to its limits, testers can identify weaknesses or points of failure that need to be addressed to ensure optimal performance under stress.

Extraction is the correct option. In the ETL (Extract, Transform, Load) process, the first step is to extract data from the source systems. This involves identifying the relevant data sources and pulling the required data into the ETL pipeline for further processing.

Common challenges in data validation during ETL processes include ensuring data quality, managing large data volumes efficiently, dealing with data latency issues, and maintaining data lineage.

Database testing verifies the accuracy, consistency, and integrity of data within applications, helping to identify and mitigate issues such as data corruption and inconsistency. It ensures that data is reliable and secure, thus reducing the risk of data-related problems impacting application functionality.

SQL is commonly used for writing test scripts in database testing because it is specifically designed for querying and manipulating data in databases. Test scripts often involve executing SQL queries to verify the functionality, performance, and integrity of database operations. SQL's syntax and capabilities make it an ideal choice for database testing tasks.

Data comparison testing involves comparing data between two systems, databases, or datasets to identify discrepancies, such as missing or duplicate records. This is crucial for ensuring data integrity and accuracy. It helps detect inconsistencies that may occur during data transfer or transformation processes. Hence, it's an essential technique in database testing for identifying data integrity violations.

SQL injection is a type of security vulnerability that occurs when a malicious SQL query is inserted into input fields of a web application. Attackers can exploit this vulnerability to gain unauthorized access to the database or manipulate its contents. By injecting malicious SQL code, attackers can bypass authentication, extract sensitive information, modify or delete data, and even execute administrative tasks on the database server. Implementing input validation, parameterized queries, and using prepared statements are common techniques to prevent SQL injection attacks.