RAG Strategies for Natural Language-Based SQL Query and REST API Call Generation

Enterprise software systems commonly expose functionality through relational databases and REST APIs, requiring users to understand schemas, endpoints, and parameters. Retrieval-augmented generation (RAG) can support natural language interfaces by grounding large language models (LLMs) in enterprise-specific documentation. We evaluate three training-free RAG configurations - Standard RAG, Relevance Filtering RAG, and Iterative Retrieval RAG - for SQL query generation, REST API call generation, and a combined task requiring routing between both operation types. Using SAP Transactional Banking, we constructed an expert-reviewed dataset with mock execution screening and compared the configurations under database-only, API-only, and mixed-documentation settings. Without retrieval, exact match accuracy is 0% across all tasks, whereas retrieval achieves mock execution success of up to 79.30% and component match accuracy of up to 78.86%. In the combined task, Iterative Retrieval RAG achieves higher exact match accuracy than Standard RAG (10.29% vs. 7.45%), with similar mock execution success (68.93% vs. 67.10%). However, for REST API call generation under mixed documentation, Iterative Retrieval RAG achieves lower mock execution success than Standard RAG (50.53% vs. 75.79%). Overall, retrieval-control strategies show task- and metric-dependent behavior under mixed-documentation settings.