.claude/rules/sql.md

@@ -61,6 +61,24 @@ Reference: vault `Pattern_CAST_AS_Type`.
 
 Reference: `93_cad_parcels_geom_multipolygon.sql` (Polygon → MultiPolygon migration).
 
+## Агрегация по pre-aggregated строкам (обязательно weighted AVG)
+
+Если источник содержит строки вида «одна строка = один период (месяц) + уже посчитанный
+`avg_value` + `count`» (например `objective_corpus_room_month`), то наивный `AVG(avg_value)`
+**неверен**: строки с нулевыми сделками занижают результат в 2-10x.
+
+Правильная формула — count-weighted AVG:
+```sql
+SUM(avg_value * cnt) / NULLIF(SUM(cnt), 0)
+```
+
+- `NULLIF(..., 0)` обязателен — предотвращает `division by zero` при all-zero периодах
+  и возвращает `NULL` вместо фейкового `0`.
+- Без весов: `AVG()` равноправно учитывает «пустые» месяцы → занижение.
+
+Reference: fix #295 (`100_fix_mv_layout_velocity_weighted_avg.sql`),
+тест `backend/tests/sql/test_mv_layout_velocity_weighted_avg.py`.
+
 ## Запреты
 
 - ❌ `DROP TABLE` / `TRUNCATE` без явного approval пользователя

backend/tests/sql/test_mv_layout_velocity_weighted_avg.py

@@ -0,0 +1,276 @@
+"""
+Regression test for fix #295 — mv_layout_velocity weighted AVG.
+
+Proves that the count-weighted formula
+    SUM(val * cnt) / NULLIF(SUM(cnt), 0)
+produces the correct result and differs from naive AVG when zero-deal months are present.
+
+Uses psycopg v3 (never psycopg2) with a temporary table containing known data.
+All bind parameters use CAST(:x AS type) — never :x::type.
+"""
+
+from decimal import Decimal
+
+import psycopg
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# Fixture: connect to the test / local DB via env-var DATABASE_URL,
+# fall back to the tunnel URL used in local dev.
+# ---------------------------------------------------------------------------
+
+def _get_dsn() -> str:
+    import os
+    return os.environ.get(
+        "DATABASE_URL",
+        "postgresql://gendesign@localhost:15432/gendesign",
+    )
+
+
+@pytest.fixture()
+def conn():
+    """Open a psycopg v3 connection and roll back after the test."""
+    with psycopg.connect(_get_dsn(), autocommit=False) as c:
+        yield c
+        c.rollback()
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+_CREATE_TEMP = """
+CREATE TEMP TABLE _test_ocm (
+    room_bucket TEXT,
+    deals_total_count INTEGER,
+    deals_total_avg_area_m2 NUMERIC,
+    deals_total_avg_price_thousand_rub_per_m2 NUMERIC
+) ON COMMIT DROP;
+"""
+
+_INSERT_ROW = """
+INSERT INTO _test_ocm VALUES (
+    CAST(%s AS text),
+    CAST(%s AS integer),
+    CAST(%s AS numeric),
+    CAST(%s AS numeric)
+);
+"""
+
+# Weighted aggregate query — mirrors the fixed mv_layout_velocity formula exactly.
+_WEIGHTED_QUERY = """
+SELECT
+    room_bucket,
+    SUM(deals_total_count)                                               AS total_deals,
+    AVG(deals_total_avg_area_m2)::numeric(10,2)                         AS naive_avg_area,
+    (SUM(deals_total_avg_area_m2 * deals_total_count)
+        / NULLIF(SUM(deals_total_count), 0))::numeric(10,2)             AS weighted_avg_area,
+    AVG(deals_total_avg_price_thousand_rub_per_m2)::numeric(12,2)       AS naive_avg_price,
+    (SUM(deals_total_avg_price_thousand_rub_per_m2 * deals_total_count)
+        / NULLIF(SUM(deals_total_count), 0))::numeric(12,2)             AS weighted_avg_price
+FROM _test_ocm
+GROUP BY room_bucket
+ORDER BY room_bucket;
+"""
+
+
+# ---------------------------------------------------------------------------
+# Test cases
+# ---------------------------------------------------------------------------
+
+class TestWeightedAvgFormula:
+    """Unit-level verification of the count-weighted formula using a temp table."""
+
+    def test_zero_deal_months_skew_naive_avg(self, conn: psycopg.Connection) -> None:
+        """
+        Scenario: studio, 3 months in window.
+          Month 1: 10 deals, avg_area=25, avg_price=180
+          Month 2:  0 deals, avg_area=0,  avg_price=0     ← zero row
+          Month 3:  0 deals, avg_area=0,  avg_price=0     ← zero row
+
+        Naive AVG: area = (25+0+0)/3 = 8.33  (wrong — dragged down by zeros)
+        Weighted:  area = (25*10) / 10 = 25   (correct)
+
+        This replicates the exact bug reported in #295.
+        """
+        with conn.cursor() as cur:
+            cur.execute(_CREATE_TEMP)
+            rows = [
+                ("studio", 10, 25.0, 180.0),
+                ("studio",  0,  0.0,   0.0),
+                ("studio",  0,  0.0,   0.0),
+            ]
+            cur.executemany(_INSERT_ROW, rows)
+            cur.execute(_WEIGHTED_QUERY)
+            result = cur.fetchone()
+
+        assert result is not None
+        room, total_deals, naive_area, weighted_area, naive_price, weighted_price = result
+
+        assert room == "studio"
+        assert total_deals == 10
+
+        # Naive AVG is wrong — zero rows drag it down
+        assert naive_area == Decimal("8.33"), (
+            f"Expected naive AVG=8.33 (showing the bug), got {naive_area}"
+        )
+        assert naive_price == Decimal("60.00"), (
+            f"Expected naive price=60.00 (showing the bug), got {naive_price}"
+        )
+
+        # Weighted AVG is correct — ignores zero-deal months
+        assert weighted_area == Decimal("25.00"), (
+            f"Expected weighted area=25.00, got {weighted_area}"
+        )
+        assert weighted_price == Decimal("180.00"), (
+            f"Expected weighted price=180.00, got {weighted_price}"
+        )
+
+        # The whole point: weighted != naive when zeros present
+        assert weighted_area != naive_area
+        assert weighted_price != naive_price
+
+    def test_weighted_differs_from_naive_sparse_project(
+        self, conn: psycopg.Connection
+    ) -> None:
+        """
+        Scenario inspired by real data: 3-room flat, project with 5 deals
+        spread across 5 active months out of 15 total months.
+
+        Mirrors the 'Vitamin-квартал на Титова' / 3-room case from prod
+        where buggy=27.14m² vs correct=81.43m² (3x undercount).
+        """
+        with conn.cursor() as cur:
+            cur.execute(_CREATE_TEMP)
+            # 10 zero-deal months + 5 active months with avg_area=81
+            rows = [("3", 0, 0.0, 0.0)] * 10 + [("3", 1, 81.0, 136.0)] * 5
+            cur.executemany(_INSERT_ROW, rows)
+            cur.execute(_WEIGHTED_QUERY)
+            result = cur.fetchone()
+
+        assert result is not None
+        room, total_deals, naive_area, weighted_area, naive_price, weighted_price = result
+
+        assert room == "3"
+        assert total_deals == 5
+
+        # Weighted: 5 deals * 81 / 5 deals = 81.00
+        assert weighted_area == Decimal("81.00")
+        assert weighted_price == Decimal("136.00")
+
+        # Naive: (10*0 + 5*81) / 15 = 27.00 — wrong
+        assert naive_area == Decimal("27.00")
+
+        # Correction factor > 2x
+        ratio = float(weighted_area) / float(naive_area)
+        assert ratio > 2.5, (
+            f"Expected correction factor > 2.5x for sparse project, got {ratio:.2f}"
+        )
+
+    def test_no_zero_months_weighted_equals_naive(
+        self, conn: psycopg.Connection
+    ) -> None:
+        """
+        When every month has deals, weighted and naive AVG should be equal
+        (within numeric(10,2) rounding) only if counts are uniform.
+        When counts differ between months, weighted still differs — and is more accurate.
+        But if all counts are equal, they match exactly.
+        """
+        with conn.cursor() as cur:
+            cur.execute(_CREATE_TEMP)
+            # All months active, same deal count → weighted == naive
+            rows = [
+                ("1", 5, 38.0, 170.0),
+                ("1", 5, 40.0, 175.0),
+                ("1", 5, 36.0, 165.0),
+            ]
+            cur.executemany(_INSERT_ROW, rows)
+            cur.execute(_WEIGHTED_QUERY)
+            result = cur.fetchone()
+
+        assert result is not None
+        _, total_deals, naive_area, weighted_area, naive_price, weighted_price = result
+
+        assert total_deals == 15
+        # With equal weights (5 each), weighted == naive
+        assert weighted_area == naive_area, (
+            f"Equal-weight case: expected weighted={naive_area}, got {weighted_area}"
+        )
+        assert weighted_price == naive_price
+
+    def test_nullif_prevents_division_by_zero(
+        self, conn: psycopg.Connection
+    ) -> None:
+        """
+        When all months have 0 deals, NULLIF(SUM(cnt), 0) → NULL instead of divide-by-zero.
+        The buggy AVG() also returns 0 (not NULL) for all-zero rows, which is arguably
+        worse — it emits a fake value rather than NULL.
+        """
+        with conn.cursor() as cur:
+            cur.execute(_CREATE_TEMP)
+            rows = [
+                ("2", 0, 0.0, 0.0),
+                ("2", 0, 0.0, 0.0),
+            ]
+            cur.executemany(_INSERT_ROW, rows)
+            cur.execute(_WEIGHTED_QUERY)
+            result = cur.fetchone()
+
+        assert result is not None
+        _, total_deals, naive_area, weighted_area, naive_price, weighted_price = result
+
+        assert total_deals == 0
+        # Weighted formula returns NULL for all-zero-deal case (correct — no real data)
+        assert weighted_area is None, (
+            f"Expected weighted_area=NULL for all-zero-deal case, got {weighted_area}"
+        )
+        assert weighted_price is None, (
+            f"Expected weighted_price=NULL for all-zero-deal case, got {weighted_price}"
+        )
+        # Naive AVG returns 0.00 — a misleading non-NULL value
+        assert naive_area == Decimal("0.00")
+
+    def test_hand_computed_weighted_average(
+        self, conn: psycopg.Connection
+    ) -> None:
+        """
+        End-to-end hand-computed check with multiple room buckets and
+        mixed deal counts to verify the formula is exactly correct.
+
+        Hand computation:
+          studio: area = (30*8 + 28*12 + 27*3) / (8+12+3) = (240+336+81)/23 = 657/23 ≈ 28.57
+                  price = (160*8 + 170*12 + 155*3) / 23 = (1280+2040+465)/23 = 3785/23 ≈ 164.57
+          1-room: area = (38*15 + 40*5) / 20 = (570+200)/20 = 770/20 = 38.50
+                  price = (175*15 + 180*5) / 20 = (2625+900)/20 = 3525/20 = 176.25
+        """
+        with conn.cursor() as cur:
+            cur.execute(_CREATE_TEMP)
+            rows = [
+                ("studio",  8, 30.0, 160.0),
+                ("studio", 12, 28.0, 170.0),
+                ("studio",  3, 27.0, 155.0),
+                ("1",      15, 38.0, 175.0),
+                ("1",       5, 40.0, 180.0),
+            ]
+            cur.executemany(_INSERT_ROW, rows)
+            cur.execute(_WEIGHTED_QUERY)
+            rows_out = cur.fetchall()
+
+        by_room = {r[0]: r for r in rows_out}
+
+        studio = by_room["studio"]
+        assert studio[3] == Decimal("28.57"), (
+            f"studio weighted_area: expected 28.57, got {studio[3]}"
+        )
+        assert studio[5] == Decimal("164.57"), (
+            f"studio weighted_price: expected 164.57, got {studio[5]}"
+        )
+
+        one_room = by_room["1"]
+        assert one_room[3] == Decimal("38.50"), (
+            f"1-room weighted_area: expected 38.50, got {one_room[3]}"
+        )
+        assert one_room[5] == Decimal("176.25"), (
+            f"1-room weighted_price: expected 176.25, got {one_room[5]}"
+        )