text: CREATE OR REPLACE FUNCTION water_class(waterway text, water text) RETURNS text AS
  $$
  SELECT CASE
             WHEN waterway='riverbank' THEN 'river'
             %%FIELD_MAPPING: class %%
             ELSE 'lake'
             END;
  $$ LANGUAGE SQL IMMUTABLE
                  PARALLEL SAFE;
  
  
  CREATE OR REPLACE FUNCTION waterway_brunnel(is_bridge bool, is_tunnel bool) RETURNS text AS
  $$
  SELECT CASE
             WHEN is_bridge THEN 'bridge'
             WHEN is_tunnel THEN 'tunnel'
             END;
  $$ LANGUAGE SQL IMMUTABLE
                  STRICT
                  PARALLEL SAFE;
  
  -- ne_10m_ocean
  -- etldoc:  ne_10m_ocean ->  ne_10m_ocean_gen_z5
  DROP MATERIALIZED VIEW IF EXISTS ne_10m_ocean_gen_z5 CASCADE;
  CREATE MATERIALIZED VIEW ne_10m_ocean_gen_z5 AS
  (
  SELECT ST_Simplify(geometry, ZRes(7)) AS geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_10m_ocean
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_10m_ocean_gen_z5_idx ON ne_10m_ocean_gen_z5 USING gist (geometry);
  
  -- ne_10m_lakes
  -- etldoc:  ne_10m_lakes ->  ne_10m_lakes_gen_z5
  DROP MATERIALIZED VIEW IF EXISTS ne_10m_lakes_gen_z5 CASCADE;
  CREATE MATERIALIZED VIEW ne_10m_lakes_gen_z5 AS
  (
  SELECT ogc_fid,
         ST_MakeValid(ST_Simplify(geometry, ZRes(7))) AS geometry,
         name,
         'lake'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_10m_lakes
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_10m_lakes_gen_z5_idx ON ne_10m_lakes_gen_z5 USING gist (geometry);
  
  -- etldoc:  ne_10m_lakes_gen_z5 ->  ne_10m_lakes_gen_z4
  DROP MATERIALIZED VIEW IF EXISTS ne_10m_lakes_gen_z4 CASCADE;
  CREATE MATERIALIZED VIEW ne_10m_lakes_gen_z4 AS
  (
  SELECT ogc_fid,
         ST_MakeValid(ST_Simplify(geometry, ZRes(6))) AS geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_10m_lakes_gen_z5
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_10m_lakes_gen_z4_idx ON ne_10m_lakes_gen_z4 USING gist (geometry);
  
  -- ne_50m_ocean
  -- etldoc:  ne_50m_ocean ->  ne_50m_ocean_gen_z4
  DROP MATERIALIZED VIEW IF EXISTS ne_50m_ocean_gen_z4 CASCADE;
  CREATE MATERIALIZED VIEW ne_50m_ocean_gen_z4 AS
  (
  SELECT ST_Simplify(geometry, ZRes(6)) AS geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_50m_ocean
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_50m_ocean_gen_z4_idx ON ne_50m_ocean_gen_z4 USING gist (geometry);
  
  -- etldoc:  ne_50m_ocean_gen_z4 ->  ne_50m_ocean_gen_z3
  DROP MATERIALIZED VIEW IF EXISTS ne_50m_ocean_gen_z3 CASCADE;
  CREATE MATERIALIZED VIEW ne_50m_ocean_gen_z3 AS
  (
  SELECT ST_Simplify(geometry, ZRes(5)) AS geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_ocean_gen_z4
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_50m_ocean_gen_z3_idx ON ne_50m_ocean_gen_z3 USING gist (geometry);
  
  -- etldoc:  ne_50m_ocean_gen_z3 ->  ne_50m_ocean_gen_z2
  DROP MATERIALIZED VIEW IF EXISTS ne_50m_ocean_gen_z2 CASCADE;
  CREATE MATERIALIZED VIEW ne_50m_ocean_gen_z2 AS
  (
  SELECT ST_Simplify(geometry, ZRes(4)) AS geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_ocean_gen_z3
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_50m_ocean_gen_z2_idx ON ne_50m_ocean_gen_z2 USING gist (geometry);
  
  -- ne_50m_lakes
  -- etldoc:  ne_50m_lakes ->  ne_50m_lakes_gen_z3
  DROP MATERIALIZED VIEW IF EXISTS ne_50m_lakes_gen_z3 CASCADE;
  CREATE MATERIALIZED VIEW ne_50m_lakes_gen_z3 AS
  (
  SELECT ogc_fid,
         ST_MakeValid(ST_Simplify(geometry, ZRes(5))) AS geometry,
         name,
         'lakes'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_50m_lakes
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_50m_lakes_gen_z3_idx ON ne_50m_lakes_gen_z3 USING gist (geometry);
  
  -- etldoc:  ne_50m_lakes_gen_z3 ->  ne_50m_lakes_gen_z2
  DROP MATERIALIZED VIEW IF EXISTS ne_50m_lakes_gen_z2 CASCADE;
  CREATE MATERIALIZED VIEW ne_50m_lakes_gen_z2 AS
  (
  SELECT ogc_fid,
         ST_MakeValid(ST_Simplify(geometry, ZRes(4))) AS geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_lakes_gen_z3
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_50m_lakes_gen_z2_idx ON ne_50m_lakes_gen_z2 USING gist (geometry);
  
  --ne_110m_ocean
  -- etldoc:  ne_110m_ocean ->  ne_110m_ocean_gen_z1
  DROP MATERIALIZED VIEW IF EXISTS ne_110m_ocean_gen_z1 CASCADE;
  CREATE MATERIALIZED VIEW ne_110m_ocean_gen_z1 AS
  (
  SELECT ST_Simplify(geometry, ZRes(3)) AS geometry,
         NULL::text AS name,
         'ocean'::text AS class,
          NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_110m_ocean
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_110m_ocean_gen_z1_idx ON ne_110m_ocean_gen_z1 USING gist (geometry);
  
  -- etldoc:  ne_110m_ocean_gen_z1 ->  ne_110m_ocean_gen_z0
  DROP MATERIALIZED VIEW IF EXISTS ne_110m_ocean_gen_z0 CASCADE;
  CREATE MATERIALIZED VIEW ne_110m_ocean_gen_z0 AS
  (
  SELECT ST_Simplify(geometry, ZRes(2)) AS geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_110m_ocean_gen_z1
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_110m_ocean_gen_z0_idx ON ne_110m_ocean_gen_z0 USING gist (geometry);
  
  
  -- ne_110m_lakes
  -- etldoc:  ne_110m_lakes ->  ne_110m_lakes_gen_z1
  DROP MATERIALIZED VIEW IF EXISTS ne_110m_lakes_gen_z1 CASCADE;
  CREATE MATERIALIZED VIEW ne_110m_lakes_gen_z1 AS
  (
  SELECT ogc_fid,
         ST_Simplify(geometry, ZRes(3)) AS geometry,
         name,
         'lakes'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM ne_110m_lakes
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_110m_lakes_gen_z1_idx ON ne_110m_lakes_gen_z1 USING gist (geometry);
  
  -- etldoc:  ne_110m_lakes_gen_z1 ->  ne_110m_lakes_gen_z0
  DROP MATERIALIZED VIEW IF EXISTS ne_110m_lakes_gen_z0 CASCADE;
  CREATE MATERIALIZED VIEW ne_110m_lakes_gen_z0 AS
  (
  SELECT ogc_fid,
         ST_Simplify(geometry, ZRes(2)) AS geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_110m_lakes_gen_z1
      ) /* DELAY_MATERIALIZED_VIEW_CREATION */ ;
  CREATE INDEX IF NOT EXISTS ne_110m_lakes_gen_z0_idx ON ne_110m_lakes_gen_z0 USING gist (geometry);
  
  
  CREATE OR REPLACE VIEW water_z0 AS
  (
  -- etldoc:  ne_110m_ocean_gen_z0 ->  water_z0
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_110m_ocean_gen_z0
  UNION ALL
  -- etldoc:  ne_110m_lakes_gen_z0 ->  water_z0
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_110m_lakes_gen_z0
      );
  
  CREATE OR REPLACE VIEW water_z1 AS
  (
  -- etldoc:  ne_110m_ocean_gen_z1 ->  water_z1
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_110m_ocean_gen_z1
  UNION ALL
  -- etldoc:  ne_110m_lakes_gen_z1 ->  water_z1
  SELECT geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
         area
  FROM ne_110m_lakes_gen_z1
      );
  
  CREATE OR REPLACE VIEW water_z2 AS
  (
  -- etldoc:  ne_50m_ocean_gen_z2 ->  water_z2
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_ocean_gen_z2
  UNION ALL
  -- etldoc:  ne_50m_lakes_gen_z2 ->  water_z2
  SELECT geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_lakes_gen_z2
      );
  
  CREATE OR REPLACE VIEW water_z3 AS
  (
  -- etldoc:  ne_50m_ocean_gen_z3 ->  water_z3
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_ocean_gen_z3
  UNION ALL
  -- etldoc:  ne_50m_lakes_gen_z3 ->  water_z3
  SELECT geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_lakes_gen_z3
      );
  
  CREATE OR REPLACE VIEW water_z4 AS
  (
  -- etldoc:  ne_50m_ocean_gen_z4 ->  water_z4
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_50m_ocean_gen_z4
  UNION ALL
  -- etldoc:  ne_10m_lakes_gen_z4 ->  water_z4
  SELECT geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_10m_lakes_gen_z4
      );
  
  CREATE OR REPLACE VIEW water_z5 AS
  (
  -- etldoc:  ne_10m_ocean_gen_z5 ->  water_z5
  SELECT geometry,
         NULL::text AS name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_10m_ocean_gen_z5
  UNION ALL
  -- etldoc:  ne_10m_lakes_gen_z5 ->  water_z5
  SELECT geometry,
         name,
         class,
         subclass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM ne_10m_lakes_gen_z5
      );
  
  CREATE OR REPLACE VIEW water_z6 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z6 ->  water_z6
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z6
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z6 ->  water_z6
  SELECT geometry,
          name,
         water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
         area
  FROM osm_water_polygon_gen_z6
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z7 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z7 ->  water_z7
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z7
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z7 ->  water_z7
  SELECT geometry,
          name,
         water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
         area
  FROM osm_water_polygon_gen_z7
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z8 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z8 ->  water_z8
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z8
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z8 ->  water_z8
  SELECT geometry,
          name,
         water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
         area
  FROM osm_water_polygon_gen_z8
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z9 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z9 ->  water_z9
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z9
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z9 ->  water_z9
  SELECT geometry,
          name,
         water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
         area
  FROM osm_water_polygon_gen_z9
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z10 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z10 ->  water_z10
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z10
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z10 ->  water_z10
  SELECT geometry,
          name,
  water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          area
  FROM osm_water_polygon_gen_z10
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z11 AS
  (
  -- etldoc:  osm_ocean_polygon_gen_z11 ->  water_z11
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_gen_z11
  UNION ALL
  -- etldoc:  osm_water_polygon_gen_z11 ->  water_z11
  SELECT geometry,
          name,
         water_class(waterway, water) AS class,
          COALESCE(
          NULLIF("landuse", ''),
          NULLIF("leisure", ''),
          NULLIF("waterway", ''),
          NULLIF("water", ''),
          NULLIF("amenity", ''),
          NULLIF("natural", '')
          ) AS sublcass,
         is_intermittent,
         NULL::boolean AS is_bridge,
          NULL::boolean AS is_tunnel,
          area
  FROM osm_water_polygon_gen_z11
  WHERE "natural" != 'bay'
      );
  
  CREATE OR REPLACE VIEW water_z12 AS
  (
  -- etldoc:  osm_ocean_polygon_union ->  water_z12
  SELECT geometry,
         NULL::text AS name,
         'ocean'::text AS class,
         NULL::text AS subclass,
         NULL::boolean AS is_intermittent,
         NULL::boolean AS is_bridge,
         NULL::boolean AS is_tunnel,
          NULL::real as area
  FROM osm_ocean_polygon_union
  UNION ALL
  -- etldoc:  osm_water_polygon ->  water_z12
  SELECT geometry,
         name,
         water_class(waterway, water) AS class,
         amenity AS sublcass,
         is_intermittent,
         is_bridge,
          is_tunnel,
          area
  FROM osm_water_polygon
  WHERE "natural" != 'bay'
      );
  
  -- etldoc: layer_water [shape=record fillcolor=lightpink, style="rounded,filled",
  -- etldoc:     label="layer_water |<z0> z0|<z1>z1|<z2>z2|<z3>z3 |<z4> z4|<z5>z5|<z6>z6|<z7>z7| <z8> z8 |<z9> z9 |<z10> z10 |<z11> z11 |<z12> z12+" ] ;
  
  CREATE OR REPLACE FUNCTION layer_water(bbox geometry, zoom_level int, pixel_width numeric, pixel_height numeric)
  RETURNS TABLE(geometry geometry, name text, class text, subclass text, brunnel text, intermittent int, way_pixels bigint) AS $$
  SELECT geometry,
         (CASE WHEN class != 'river' THEN  NULLIF(name::text, '') ELSE NULL END)::text AS name,
         class::text,
         (CASE WHEN subclass = class THEN NULL ELSE subclass END)::text,
         waterway_brunnel(is_bridge, is_tunnel) AS brunnel,
          NULLIF(is_intermittent,false)::int AS intermittent,
         (CASE WHEN area IS NOT NULL AND class != 'river' THEN NULLIF((area/NULLIF(zoom_level::real*pixel_width::real*pixel_height::real,0))::bigint, 0) ELSE NULL END)::bigint AS way_pixels
  FROM (
           -- etldoc: water_z0 ->  layer_water:z0
           SELECT *
           FROM water_z0
           WHERE zoom_level = 0
           UNION ALL
           -- etldoc: water_z1 ->  layer_water:z1
           SELECT *
           FROM water_z1
           WHERE zoom_level = 1
           UNION ALL
           -- etldoc: water_z2 ->  layer_water:z2
           SELECT *
           FROM water_z2
           WHERE zoom_level = 2
           UNION ALL
           -- etldoc: water_z3 ->  layer_water:z3
           SELECT *
           FROM water_z3
           WHERE zoom_level = 3
           UNION ALL
           -- etldoc: water_z4 ->  layer_water:z4
           SELECT *
           FROM water_z4
           WHERE zoom_level = 4
           UNION ALL
           -- etldoc: water_z5 ->  layer_water:z5
           SELECT *
           FROM water_z5
           WHERE zoom_level = 5
           UNION ALL
           -- etldoc: water_z6 ->  layer_water:z6
           SELECT *
           FROM water_z6
           WHERE zoom_level = 6
           UNION ALL
           -- etldoc: water_z7 ->  layer_water:z7
           SELECT *
           FROM water_z7
           WHERE zoom_level = 7
           UNION ALL
           -- etldoc: water_z8 ->  layer_water:z8
           SELECT *
           FROM water_z8
           WHERE zoom_level = 8
           UNION ALL
           -- etldoc: water_z9 ->  layer_water:z9
           SELECT *
           FROM water_z9
           WHERE zoom_level = 9
           UNION ALL
           -- etldoc: water_z10 ->  layer_water:z10
           SELECT *
           FROM water_z10
           WHERE zoom_level = 10
           UNION ALL
           -- etldoc: water_z11 ->  layer_water:z11
           SELECT *
           FROM water_z11
           WHERE zoom_level = 11
           UNION ALL
           -- etldoc: water_z12 ->  layer_water:z12
           SELECT *
           FROM water_z12
           WHERE zoom_level >= 12
       ) AS zoom_levels
  WHERE geometry && bbox;
  $$ LANGUAGE SQL STABLE
                  -- STRICT
                  PARALLEL SAFE;
  