Which of the following can enhance the efficiency of ABAP managed database procedures?

Reducing code complexity is a key factor in enhancing the efficiency of ABAP managed database procedures. Streamlined, simpler code tends to execute faster and is easier to maintain. When the logic of the code isn't overly complicated, it generally results in fewer processing cycles, which positively impacts performance. Simplifying the code also simplifies debugging and future modifications, ensuring that changes do not inadvertently introduce inefficiencies.

Options that involve embedding all data directly in the procedure can lead to increased redundancy and larger code sizes, which may negatively impact performance and maintainability. Using outdated coding standards usually goes against best practices, potentially resulting in less optimized code. Ignoring performance optimization can significantly decrease the efficiency of database procedures, as performance tuning is vital for optimizing execution time and resource usage. Thus, reducing code complexity stands out as the best practice for enhancing efficiency in ABAP managed database procedures.