fix(BUG-01b): aggregate trips and alarms in separate CTEs to avoid cartesian explosion

The original refresh_daily_metrics() joined trips × alarms in one SELECT,
producing one row per (trip, alarm) pair. Every SUM/COUNT over trip
columns was multiplied by the per-IMEI alarm count, so spot-checks
showed total_trips identical to alarm_count, drive_hours > 1000/day,
and distance_km in the tens of thousands per vehicle per day.

Migration 08 carried that flawed join forward when fixing the
TEXT→INTEGER vehicle_key crash. Rewriting the function so trip_agg and
alarm_agg are computed in separate CTEs and then joined on imei
restores correct per-vehicle aggregates: total_trips reflects real trip
count, drive_hours ≤ 24, alarms are counted once.

This bug is being fixed in the same migration file (08) before PR #12
merges; no deploy has applied the prior version, so no second migration
is needed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

08_fix_etl_vehicle_key.sql

@@ -1,15 +1,22 @@
 -- 08_fix_etl_vehicle_key.sql
--- Fixes BUG-01: dwh_gold.refresh_daily_metrics() inserted t.imei (TEXT) into
--- fact_daily_fleet_metrics.vehicle_key (INTEGER REFERENCES dim_vehicles), so
--- every nightly call raised "invalid input syntax for type integer".
+-- Fixes two distinct bugs in dwh_gold.refresh_daily_metrics():
 --
--- The fix has two parts:
---   1. Seed dwh_gold.dim_vehicles from tracksolid.devices so every IMEI has
---      a serial vehicle_key to point at.
---   2. Rewrite refresh_daily_metrics() to JOIN through dim_vehicles and
---      SELECT the serial key instead of the raw IMEI. The function also
---      upserts dim_vehicles at the top of each run so newly-registered
---      devices appear in the warehouse without manual intervention.
+-- BUG-01a (type crash): the original function inserted t.imei (TEXT) into
+-- fact_daily_fleet_metrics.vehicle_key (INTEGER REFERENCES dim_vehicles),
+-- so every nightly call raised "invalid input syntax for type integer".
+--
+-- BUG-01b (cartesian explosion): the original function joined
+-- trips × alarms in a single SELECT. For every trip row it produced one
+-- output row per matching alarm, multiplying every SUM/COUNT over trip
+-- columns by the per-IMEI alarm count. Spot-checking the broken output
+-- showed total_trips identical to alarm_count and drive_hours > 1000/day.
+--
+-- The fix has three parts:
+--   1. Seed dwh_gold.dim_vehicles from tracksolid.devices so every IMEI
+--      has a serial vehicle_key to point at.
+--   2. Rewrite refresh_daily_metrics() so trip aggregates and alarm
+--      aggregates are computed in separate CTEs and then joined on imei.
+--   3. Map IMEI → vehicle_key via dim_vehicles inside the same statement.
 
 BEGIN;
 
@@ -43,6 +50,34 @@ BEGIN
     vehicle_number = EXCLUDED.vehicle_number,
     is_active      = EXCLUDED.is_active;
 
+  -- Aggregate trips and alarms in separate CTEs to avoid the cartesian
+  -- multiplication that the original single-SELECT version produced.
+  WITH trip_agg AS (
+    SELECT
+      t.imei,
+      SUM(t.distance_km)                                       AS total_distance_km,
+      COUNT(*)                                                 AS total_trips,
+      SUM(t.driving_time_s)                                    AS total_drive_seconds,
+      SUM(t.idle_time_s)                                       AS total_idle_seconds,
+      SUM(t.fuel_consumed_l)                                   AS fuel_consumed_l,
+      MIN(t.start_time AT TIME ZONE 'Africa/Nairobi')::TIME    AS day_start_time,
+      MAX(t.end_time   AT TIME ZONE 'Africa/Nairobi')::TIME    AS day_end_time,
+      AVG(t.avg_speed_kmh)                                     AS avg_speed_kmh,
+      MAX(t.max_speed_kmh)                                     AS peak_speed_kmh
+    FROM tracksolid.trips t
+    WHERE DATE(t.start_time AT TIME ZONE 'Africa/Nairobi') = target_date
+      AND t.end_time IS NOT NULL
+    GROUP BY t.imei
+  ),
+  alarm_agg AS (
+    SELECT
+      a.imei,
+      COUNT(*)                                                AS alarm_count,
+      COUNT(*) FILTER (WHERE a.alarm_type ILIKE '%speed%')    AS overspeed_count
+    FROM tracksolid.alarms a
+    WHERE DATE(a.alarm_time AT TIME ZONE 'Africa/Nairobi') = target_date
+    GROUP BY a.imei
+  )
   INSERT INTO dwh_gold.fact_daily_fleet_metrics (
     day,
     vehicle_key,
@@ -61,26 +96,20 @@ BEGIN
   SELECT
     target_date                                                 AS day,
     dv.vehicle_key                                              AS vehicle_key,
-    ROUND(SUM(t.distance_km)::numeric, 3)                                 AS total_distance_km,
-    COUNT(*)                                                              AS total_trips,
-    ROUND((SUM(t.driving_time_s) / 3600.0)::numeric, 2)                   AS total_drive_hours,
-    ROUND((SUM(t.idle_time_s)    / 3600.0)::numeric, 2)                   AS total_idle_hours,
-    ROUND(SUM(t.fuel_consumed_l)::numeric, 3)                             AS fuel_consumed_l,
-    COUNT(a.id)                                                           AS alarm_count,
-    COUNT(a.id) FILTER (WHERE a.alarm_type ILIKE '%speed%')               AS overspeed_count,
-    MIN(t.start_time AT TIME ZONE 'Africa/Nairobi')::TIME                 AS day_start_time,
-    MAX(t.end_time   AT TIME ZONE 'Africa/Nairobi')::TIME                 AS day_end_time,
-    ROUND(AVG(t.avg_speed_kmh)::numeric, 2)                               AS avg_speed_kmh,
-    MAX(t.max_speed_kmh)                                                  AS peak_speed_kmh
-  FROM tracksolid.trips t
-  JOIN dwh_gold.dim_vehicles dv
-    ON dv.imei = t.imei
-  LEFT JOIN tracksolid.alarms a
-    ON  a.imei = t.imei
-    AND DATE(a.alarm_time AT TIME ZONE 'Africa/Nairobi') = target_date
-  WHERE DATE(t.start_time AT TIME ZONE 'Africa/Nairobi') = target_date
-    AND t.end_time IS NOT NULL
-  GROUP BY dv.vehicle_key
+    ROUND(tr.total_distance_km::numeric, 3)                     AS total_distance_km,
+    tr.total_trips                                              AS total_trips,
+    ROUND((tr.total_drive_seconds / 3600.0)::numeric, 2)        AS total_drive_hours,
+    ROUND((tr.total_idle_seconds  / 3600.0)::numeric, 2)        AS total_idle_hours,
+    ROUND(tr.fuel_consumed_l::numeric, 3)                       AS fuel_consumed_l,
+    COALESCE(al.alarm_count, 0)                                 AS alarm_count,
+    COALESCE(al.overspeed_count, 0)                             AS overspeed_count,
+    tr.day_start_time                                           AS day_start_time,
+    tr.day_end_time                                             AS day_end_time,
+    ROUND(tr.avg_speed_kmh::numeric, 2)                         AS avg_speed_kmh,
+    tr.peak_speed_kmh                                           AS peak_speed_kmh
+  FROM trip_agg tr
+  JOIN dwh_gold.dim_vehicles dv ON dv.imei = tr.imei
+  LEFT JOIN alarm_agg al       ON al.imei = tr.imei
   ON CONFLICT (day, vehicle_key) DO UPDATE SET
     total_distance_km = EXCLUDED.total_distance_km,
     total_trips       = EXCLUDED.total_trips,
@@ -98,7 +127,8 @@ $$;
 
 COMMENT ON FUNCTION dwh_gold.refresh_daily_metrics(DATE)
   IS 'Populates or refreshes fact_daily_fleet_metrics for the given date. '
-     'Joins tracksolid.trips through dwh_gold.dim_vehicles to map IMEI → vehicle_key. '
+     'Trips and alarms are aggregated in separate CTEs to avoid cartesian '
+     'multiplication. Maps IMEI → vehicle_key via dwh_gold.dim_vehicles. '
      'Call nightly: SELECT dwh_gold.refresh_daily_metrics(CURRENT_DATE - 1);';
 
 COMMIT;