Convert semi-colon separated house numbers to a range

layers/housenumber/housenumber.sql

@@ -14,7 +14,7 @@ SELECT
     -- etldoc: osm_housenumber_point -> layer_housenumber:z14_
     osm_id,
     geometry,
-    housenumber
+    display_housenumber(housenumber)
 FROM (
     SELECT
         osm_id,

layers/housenumber/housenumber.yaml

@@ -7,12 +7,14 @@ layer:
   buffer_size: 8
   srs: +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over
   fields:
-    housenumber: Value of the [`addr:housenumber`](http://wiki.openstreetmap.org/wiki/Key:addr) tag.
+    housenumber: Value of the [`addr:housenumber`](http://wiki.openstreetmap.org/wiki/Key:addr) tag. 
+      If there are multiple values separated by semi-colons, the first and last value separated by a dash.
   datasource:
     geometry_field: geometry
     srid: 900913
     query: (SELECT geometry, housenumber FROM layer_housenumber(!bbox!, z(!scale_denominator!))) AS t
 schema:
+  - ./housenumber_display.sql
   - ./housenumber_centroid.sql
   - ./housenumber.sql
 datasources:

layers/housenumber/housenumber_display.sql

@@ -0,0 +1,20 @@
+CREATE OR REPLACE FUNCTION display_housenumber_nonnumeric(raw_housenumber text)
+RETURNS text AS $$
+  -- Find the position of the semicolon in the input string
+  -- and extract the first and last value
+  SELECT substring(raw_housenumber from 1 for position(';' in raw_housenumber) - 1)
+         || '–'
+         || substring(raw_housenumber from position(';' in raw_housenumber) + 1);
+$$ LANGUAGE SQL IMMUTABLE;
+
+
+CREATE OR REPLACE FUNCTION display_housenumber(raw_housenumber text)
+RETURNS text AS $$
+  SELECT CASE
+    WHEN raw_housenumber !~ ';' THEN raw_housenumber
+    WHEN raw_housenumber ~ '[^0-9;]' THEN display_housenumber_nonnumeric(raw_housenumber)
+    ELSE
+      (SELECT min(value)::text || '–' || max(value)::text
+       FROM unnest(string_to_array(raw_housenumber, ';')::int[]) AS value)
+  END
+$$ LANGUAGE SQL IMMUTABLE;