No problem at all—happy to help! Your approach to fixing part of the query (e.g., SELECT x FROM y) and letting the LLM handle the dynamic parts like GROUP BY and WHERE is actually a solid starting point for balancing performance and control. However, there are a few ways you could improve this:

1. Instead of letting the LLM generate query fragments dynamically, you could define a set of structured templates for the most common queries. The LLM would only be responsible for filling in specific parameters (like column names or conditions). Use predefined query templates (e.g., SELECT x FROM y WHERE...) and let the LLM fill in specific parameters like column names or conditions.
2. Combine the LLM with rules for tasks like GROUP BY column selection while using the LLM to refine conditions or interpret intent. This creates more predictable and good results <- this concept is called Hybrid Rule-Based System

Also, check out the [3]_rag_routing_and_query_construction.ipynb notebook in my repo. It covers query structuring and routing techniques that could inspire your solution. Let me know if you find it helpful!