Improved Join Order Optimization for Database Queries using Hybrid Quantum-Classical Approaches for QUBO Problems

2026-06-15

AI Summary

This study addresses the join ordering problem for complex queries in relational databases by proposing a novel approach that integrates Elimination of Cartesian Products (ECP) with QUBO Search Space Splitting (SQSS) to substantially reduce the size of the QUBO formulation, thereby decreasing the number of variables and constraints. Building on this compact representation, the authors systematically evaluate the performance of hybrid quantum-classical algorithms—including Quantum Annealing (QA), Simulated Annealing (SA), QAOA, and VQE—on real-world SQL queries. Experimental results demonstrate that the proposed method consistently yields optimal join orders across varying selectivity rates, significantly improving query execution efficiency. The study also highlights the current limitations of existing quantum hardware when applied to complex query optimization tasks.

Abstract

Efficient query optimization is crucial for relational database systems, especially for optimizing join orders in complex queries. This work introduces a hybrid approach that integrates Eliminating Cartesian Products (ECP) with splitting the QUBO search space (SQSS) to reduce the size of the QUBO problem, minimizing binary variables and constraints. This improves the performance of the quantum algorithm while lowering hardware requirements. We evaluate our method using real-world SQL queries from the ErgastF1 dataset on quantum and classical algorithms, including Quantum Annealing (QA), Simulated Annealing (SA), QAOA, and VQE, implemented on D-Wave's Quantum Annealer and universal gate-based simulators. Additionally, we analyze the impact of selectivity and SQSS on QUBO weight distribution and algorithmic performance, highlighting optimization efficiency for QA and SA. Experimental results show consistent optimal join orders and enhanced query optimization for various selectivity conditions, and they also highlight the limitations of current quantum hardware for complex queries. This study further confirms the potential of hybrid quantum-classical methods for scalable quantum-enhanced database optimization.

Problem

• join order optimization
• query optimization
• QUBO
• relational databases
• complex queries

Innovation

• Hybrid Quantum-Classical
• QUBO
• Join Order Optimization
• Quantum Annealing
• Search Space Splitting