The Proxy design pattern acts as a surrogate or placeholder for another object and controls access to it. On the other hand, the Decorator pattern dynamically adds new functionality to an object without altering its structure. Proxy focuses on controlling access, while Decorator focuses on adding responsibilities. Understanding these distinctions is crucial when deciding which pattern to use in a given context.

Merge sort has the best time complexity in the worst-case scenario among the given options. It has a time complexity of O(n log n) in all cases, making it efficient for large datasets. Quick sort can have a worst-case time complexity of O(n^2) in certain scenarios, making it less preferable for worst-case scenarios compared to merge sort.

Option 1 is correct. In an e-commerce application, optimizing queries for product recommendations involves indexing relevant attributes like product categories, user preferences, and purchase history. This speeds up retrieval by reducing search times. Query optimization techniques further enhance performance. NoSQL databases may offer scalability benefits but might not align with RDBMS concepts directly. Caching can improve performance but is secondary to optimizing queries. Complex SQL queries and normalization may not be optimal for recommendation systems due to performance overhead and complexity.

The correct option is "Capacity." In arrays, capacity refers to the total number of elements that can be stored. It is determined during the array's initialization and remains fixed unless the array is resized. The capacity of an array is distinct from its size, which refers to the number of elements currently stored in the array. Understanding the capacity is crucial for managing memory efficiently when working with arrays.

JSON Web Tokens (JWT) are compact, self-contained tokens used for authentication in web apps. They are signed to ensure integrity and can carry user identity and other claims securely. OAuth tokens are different from JWTs, used for access delegation, while JWTs are used for stateful authentication. JWTs are often employed for session management, allowing servers to verify user authenticity and authorize access to resources securely.

Cursor-based pagination using a timestamp or unique identifier is efficient for handling large datasets as it ensures stable pagination results even if items are added or removed. It also reduces the chances of duplicate or missing data during pagination.

The EVALUATE statement in COBOL is ideal for handling complex decision-making with multiple conditions, making it suitable for determining account types and applying specific rules in a bank program.

One common technique for identifying duplicate records is comparing key fields. By comparing specific fields within the records, you can identify duplicates based on the values in those fields. This is often done using logic within the COBOL program.

In COBOL, the WORKING-STORAGE section is commonly used to define the structure of data retrieved from a database. It includes variables that hold data during program execution.

The primary purpose of debugging in COBOL programming is to identify and correct errors or defects in the program. It involves the process of finding and fixing mistakes that prevent the program from running correctly.