Omair Afzal 715b81c86b fix(python): graceful handling of empty result sets in hybrid search (#3030)
## Problem

When applying hard filters that result in zero matches, hybrid search
crashes with `IndexError: list index out of range` during reranking.
This happens because empty result tables are passed through the full
reranker pipeline, which expects at least one result.

Traceback from the issue:
```
lancedb/query.py: in _combine_hybrid_results
    results = reranker.rerank_hybrid(fts_query, vector_results, fts_results)
lancedb/rerankers/answerdotai.py: in rerank_hybrid
    combined_results = self._rerank(combined_results, query)
...
IndexError: list index out of range
```

## Fix

Added an early return in `_combine_hybrid_results` when both vector and
FTS results are empty. Instead of passing empty tables through
normalization, reranking, and score restoration (which can fail in
various ways), we now build a properly-typed empty result table with the
`_relevance_score` column and return it directly.

## Test

Added `test_empty_hybrid_result_reranker` that exercises
`_combine_hybrid_results` directly with empty vector and FTS tables,
verifying:
- Returns empty table with correct schema  
- Includes `_relevance_score` column
- Respects `with_row_ids` flag

Closes #2425
2026-02-17 11:37:10 -08:00
2023-03-17 18:15:19 -07:00
2025-03-10 09:01:23 -07:00

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