naive AVG() over objective_corpus_room_month rows gives equal weight to
zero-deal months, diluting per-project averages by 2-10x. Projects with
sparse deal history (e.g. 5 active months out of 24) were shown avg_area
≈27m² instead of the correct ≈81m² for 3-room flats.
Replace both aggregates with SUM(val*cnt)/NULLIF(SUM(cnt),0) so only
months with actual deals contribute weight. NULLIF prevents division-by-zero
and returns NULL for all-zero projects instead of a misleading 0.
Prod check (Vitamin-квартал на Титова, last 24 mo): studio 26m²/176k,
1-rm 37m²/174k, 2-rm 56m²/135k, 3-rm 81m²/136k — matches expected ranges.
