feat: expand dbt models

dbt/models/marts/funda_city_stats.sql

@@ -0,0 +1,29 @@
+-- Mart: per-city price statistics for available listings.
+
+with listings as (
+    select * from {{ ref('funda_listings') }}
+    where not is_sold
+),
+
+city_stats as (
+    select
+        city,
+        province,
+        offering_type,
+        object_type,
+        count(*) as listing_count,
+        round(avg(current_price), 0) as avg_price,
+        min(current_price) as min_price,
+        max(current_price) as max_price,
+        percentile_cont(0.5) within group (
+            order by current_price
+        ) as median_price,
+        round(avg(price_per_sqm), 0) as avg_price_per_sqm,
+        round(avg(living_area), 0) as avg_living_area,
+        round(avg(bedrooms), 1) as avg_bedrooms
+    from listings
+    where current_price is not null
+    group by city, province, offering_type, object_type
+)
+
+select * from city_stats