User-defined functions in DB2 can encapsulate procedural logic for reuse in queries. This means that developers can implement custom logic within functions to perform specific operations, such as calculations, data transformations, or validations, and then reuse these functions in various SQL queries, enhancing code readability and maintainability. 

Indexing contributes to query optimization in DB2 by organizing data in a structured way, allowing the database engine to efficiently locate and retrieve data, thereby improving query performance. It helps in reducing the number of rows scanned during query execution, resulting in faster response times. 

Locking in DB2 serves the purpose of preventing concurrent transactions from accessing the same data concurrently, ensuring data integrity and consistency. This helps in avoiding situations such as dirty reads and conflicting updates, thereby maintaining the accuracy and reliability of the data. It ensures that only one transaction can modify data at a time, preventing inconsistencies. 

The First Normal Form (1NF) ensures that there are no repeating groups in a table by ensuring that each column contains atomic values, and each column has a unique name. This is the fundamental level of normalization in DB2. 

Referential integrity is the DB2 feature that helps to enforce data integrity by automatically updating related data. When a foreign key in one table references a primary key in another table, referential integrity ensures that the relationships between the tables are maintained. This means that if a record in the parent table is deleted or updated, the corresponding records in the child table are also updated or deleted to maintain consistency. By automatically updating related data, referential integrity helps prevent orphan records and ensures that the data remains accurate and consistent throughout the database. 

The EXISTS keyword in DB2 is typically used in conjunction with a SELECT statement to test for the existence of rows in the result set of a subquery. It returns true if the subquery returns any rows, otherwise false. 

Considering DB2 editions and versions during the initial planning phase of a new application is crucial for ensuring optimal performance, scalability, and compatibility with the chosen database platform. By addressing these considerations early in the development lifecycle, the software development team can avoid potential pitfalls, streamline integration efforts, and maximize the value of their database investment, ultimately contributing to the success of the application project. 

The ORDER BY clause in a SELECT statement is used to sort the result set based on one or more columns either in ascending (default) or descending order. It arranges the rows returned by the query in a specified order, making it easier for users to analyze the data. 

In a RIGHT JOIN operation, all rows from the right table are retained in the result set, even if there are no matching rows in the left table. This ensures that data from the right table is included in the output, regardless of matching criteria. 

The UNLOAD utility in DB2 is specifically designed for extracting data from DB2 tables and writing it to an external file. It allows users to export data in various formats, such as delimited text files or binary files, making it suitable for data exchange and backup purposes. The UNLOAD utility offers flexibility and efficiency in extracting large volumes of data from DB2 tables.