text: CREATE OR REPLACE FUNCTION water_class(waterway TEXT) RETURNS TEXT AS $$
      SELECT CASE WHEN waterway='' THEN 'lake' ELSE 'river' END;
  $$ LANGUAGE SQL IMMUTABLE;
  
  
  
  CREATE OR REPLACE VIEW water_z0 AS (
      -- etldoc:  ne_110m_ocean ->  water_z0
      SELECT geometry, 'ocean'::text AS class FROM ne_110m_ocean
      UNION ALL
      -- etldoc:  ne_110m_lakes ->  water_z0
      SELECT geometry, 'lake'::text AS class FROM ne_110m_lakes
  );
  
  CREATE OR REPLACE VIEW water_z1 AS (
      -- etldoc:  ne_110m_ocean ->  water_z1
      SELECT geometry, 'ocean'::text AS class FROM ne_110m_ocean
      UNION ALL
      -- etldoc:  ne_110m_lakes ->  water_z1
      SELECT geometry, 'lake'::text AS class FROM ne_110m_lakes
  );
  
  CREATE OR REPLACE VIEW water_z2 AS (
      -- etldoc:  ne_50m_ocean ->  water_z2
      SELECT geometry, 'ocean'::text AS class FROM ne_50m_ocean
      UNION ALL
      -- etldoc:  ne_50m_lakes ->  water_z2
      SELECT geometry, 'lake'::text AS class FROM ne_50m_lakes
  );
  
  CREATE OR REPLACE VIEW water_z4 AS (
      -- etldoc:  ne_50m_ocean ->  water_z4
      SELECT geometry, 'ocean'::text AS class FROM ne_50m_ocean
      UNION ALL
      -- etldoc:  ne_50m_lakes ->  water_z4
      SELECT geometry, 'lake'::text AS class FROM ne_50m_lakes
  );
  
  CREATE OR REPLACE VIEW water_z5 AS (
      -- etldoc:  ne_10m_ocean ->  water_z5
      SELECT geometry, 'ocean'::text AS class FROM ne_10m_ocean
      UNION ALL
      -- etldoc:  ne_10m_lakes ->  water_z5
      SELECT geometry, 'lake'::text AS class FROM ne_10m_lakes
  );
  
  CREATE OR REPLACE VIEW water_z6 AS (
      -- etldoc:  ne_10m_ocean ->  water_z6
      SELECT geometry, 'ocean'::text AS class FROM ne_10m_ocean
      UNION ALL
     -- etldoc:  osm_water_polygon_gen6 ->  water_z6
      SELECT geometry, 'lake' AS class FROM osm_water_polygon_gen6
  );
  
  CREATE OR REPLACE VIEW water_z7 AS (
      -- etldoc:  ne_10m_ocean ->  water_z7
      SELECT geometry, 'ocean'::text AS class FROM ne_10m_ocean
      UNION ALL
      -- etldoc:  osm_water_polygon_gen5 ->  water_z7
      SELECT geometry, 'lake' AS class FROM osm_water_polygon_gen5
  );
  
  CREATE OR REPLACE VIEW water_z8 AS (
      -- etldoc:  osm_ocean_polygon_gen4 ->  water_z8
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon_gen4
      UNION ALL
      -- etldoc:  osm_water_polygon_gen4 ->  water_z8
      SELECT geometry, 'lake' AS class FROM osm_water_polygon_gen4
  );
  
  CREATE OR REPLACE VIEW water_z9 AS (
      -- etldoc:  osm_ocean_polygon_gen3 ->  water_z9
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon_gen3
      UNION ALL
      -- etldoc:  osm_water_polygon_gen3 ->  water_z9
      SELECT geometry, 'lake'::text AS class FROM osm_water_polygon_gen3
  );
  
  CREATE OR REPLACE VIEW water_z10 AS (
      -- etldoc:  osm_ocean_polygon_gen2 ->  water_z10
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon_gen2
      UNION ALL
      -- etldoc:  osm_water_polygon_gen2 ->  water_z10
      SELECT geometry, 'lake'::text AS class FROM osm_water_polygon_gen2
  );
  
  CREATE OR REPLACE VIEW water_z11 AS (
      -- etldoc:  osm_ocean_polygon_gen1 ->  water_z11
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon_gen1
      UNION ALL
      -- etldoc:  osm_water_polygon_gen1 ->  water_z11
      SELECT geometry, water_class(waterway) AS class FROM osm_water_polygon_gen1
  );
  
  CREATE OR REPLACE VIEW water_z12 AS (
      -- etldoc:  osm_ocean_polygon_gen1 ->  water_z12
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon
      UNION ALL
      -- etldoc:  osm_water_polygon ->  water_z12
      SELECT geometry, water_class(waterway) AS class FROM osm_water_polygon
  );
  
  CREATE OR REPLACE VIEW water_z13 AS (
      -- etldoc:  osm_ocean_polygon ->  water_z13
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon
      UNION ALL
      -- etldoc:  osm_water_polygon ->  water_z13
      SELECT geometry, water_class(waterway) AS class FROM osm_water_polygon
  );
  
  CREATE OR REPLACE VIEW water_z14 AS (
      -- etldoc:  osm_ocean_polygon ->  water_z14
      SELECT geometry, 'ocean'::text AS class FROM osm_ocean_polygon
      UNION ALL
      -- etldoc:  osm_water_polygon ->  water_z14
      SELECT geometry, water_class(waterway) AS class FROM osm_water_polygon
  );
  
  -- 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|<z13> z13|<z14_> z14+" ] ;
  
  CREATE OR REPLACE FUNCTION layer_water (bbox geometry, zoom_level int)
  RETURNS TABLE(geometry geometry, class text) AS $$
      SELECT geometry, class::text FROM (
          -- etldoc: water_z0 ->  layer_water:z0
          SELECT * FROM water_z0 WHERE zoom_level = 0
          UNION ALL
          -- etldoc: water_z1 ->  layer_water:z1
          SELECT * FROM water_z1 WHERE zoom_level = 1
          UNION ALL
          -- etldoc: water_z2 ->  layer_water:z2
          -- etldoc: water_z2 ->  layer_water:z3
          SELECT * FROM water_z2 WHERE zoom_level BETWEEN 2 AND 3
          UNION ALL
          -- etldoc: water_z4 ->  layer_water:z4
          SELECT * FROM water_z4 WHERE zoom_level = 4
          UNION ALL
          -- etldoc: water_z5 ->  layer_water:z5
          SELECT * FROM water_z5 WHERE zoom_level = 5
          UNION ALL
          -- etldoc: water_z6 ->  layer_water:z6
          SELECT * FROM water_z6 WHERE zoom_level = 6
          UNION ALL
          -- etldoc: water_z7 ->  layer_water:z7
          SELECT * FROM water_z7 WHERE zoom_level = 7
          UNION ALL
          -- etldoc: water_z8 ->  layer_water:z8
          SELECT * FROM water_z8 WHERE zoom_level = 8
          UNION ALL
          -- etldoc: water_z9 ->  layer_water:z9
          SELECT * FROM water_z9 WHERE zoom_level = 9
          UNION ALL
          -- etldoc: water_z10 ->  layer_water:z10
          SELECT * FROM water_z10 WHERE zoom_level = 10
          UNION ALL
          -- etldoc: water_z11 ->  layer_water:z11
          SELECT * FROM water_z11 WHERE zoom_level = 11
          UNION ALL
          -- etldoc: water_z12 ->  layer_water:z12
          SELECT * FROM water_z12 WHERE zoom_level = 12
          UNION ALL
          -- etldoc: water_z13 ->  layer_water:z13
          SELECT * FROM water_z13 WHERE zoom_level = 13
          UNION ALL
          -- etldoc: water_z14 ->  layer_water:z14_
          SELECT * FROM water_z14 WHERE zoom_level >= 14
      ) AS zoom_levels
      WHERE geometry && bbox;
  $$ LANGUAGE SQL IMMUTABLE;
  