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Wrong fieldnames in queries related to region, road and building tables.
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The geometry field is named 'geom' (and not 'the_geom') in .shp files and so are they in the resultant tables after import.
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a-lambda authored and github-actions[bot] committed Nov 22, 2024
1 parent 48504cf commit a74600c
Showing 1 changed file with 25 additions and 25 deletions.
50 changes: 25 additions & 25 deletions docs/training_manual/spatial_databases/spatial_queries.rst
Original file line number Diff line number Diff line change
Expand Up @@ -152,9 +152,9 @@ Get all the buildings in the KwaZulu region:

.. code-block:: sql
SELECT a.id, a.name, st_astext(a.the_geom) as point
SELECT a.id, a.name, st_astext(a.geom) as point
FROM building a, region b
WHERE st_within(a.the_geom, b.the_geom)
WHERE st_within(a.geom, b.geom)
AND b.name = 'KwaZulu';
Result:
Expand All @@ -175,9 +175,9 @@ Or, if we create a view from it:
.. code-block:: sql
CREATE VIEW vw_select_location AS
SELECT a.gid, a.name, a.the_geom
SELECT a.gid, a.name, a.geom
FROM building a, region b
WHERE st_within(a.the_geom, b.the_geom)
WHERE st_within(a.geom, b.geom)
AND b.name = 'KwaZulu';
Add the view as a layer and view it in QGIS:
Expand All @@ -194,7 +194,7 @@ Show a list of all the names of regions adjoining the Hokkaido region:
SELECT b.name
FROM region a, region b
WHERE st_touches(a.the_geom, b.the_geom)
WHERE st_touches(a.geom, b.geom)
AND a.name = 'Hokkaido';
Result:
Expand All @@ -213,9 +213,9 @@ As a view:
.. code-block:: sql
CREATE VIEW vw_regions_adjoining_hokkaido AS
SELECT b.gid, b.name, b.the_geom
SELECT b.gid, b.name, b.geom
FROM region a, region b
WHERE st_touches(a.the_geom, b.the_geom)
WHERE st_touches(a.geom, b.geom)
AND a.name = 'Hokkaido';
In QGIS:
Expand All @@ -231,7 +231,7 @@ could use a buffer intersect instead:
.. code-block:: sql
CREATE VIEW vw_hokkaido_buffer AS
SELECT gid, ST_BUFFER(the_geom, 100) as the_geom
SELECT gid, ST_BUFFER(geom, 100) as geom
FROM region
WHERE name = 'Hokkaido';
Expand All @@ -247,18 +247,18 @@ Select using the buffer:
.. code-block:: sql
CREATE VIEW vw_hokkaido_buffer_select AS
SELECT b.gid, b.name, b.the_geom
SELECT b.gid, b.name, b.geom
FROM
(
SELECT * FROM
vw_hokkaido_buffer
) a,
region b
WHERE ST_INTERSECTS(a.the_geom, b.the_geom)
WHERE ST_INTERSECTS(a.geom, b.geom)
AND b.name != 'Hokkaido';
In this query, the original buffer view is used as any other table would be. It
is given the alias :kbd:`a`, and its geometry field, :kbd:`a.the_geom`, is used
is given the alias :kbd:`a`, and its geometry field, :kbd:`a.geom`, is used
to select any polygon in the :kbd:`region` table (alias :kbd:`b`) that
intersects it. However, Hokkaido itself is excluded from this select statement,
because we don't want it; we only want the regions adjoining it.
Expand All @@ -274,9 +274,9 @@ extra step of creating a buffer:
.. code-block:: sql
CREATE VIEW vw_hokkaido_distance_select AS
SELECT b.gid, b.name, b.the_geom
SELECT b.gid, b.name, b.geom
FROM region a, region b
WHERE ST_DISTANCE (a.the_geom, b.the_geom) < 100
WHERE ST_DISTANCE (a.geom, b.geom) < 100
AND a.name = 'Hokkaido'
AND b.name != 'Hokkaido';
Expand All @@ -295,7 +295,7 @@ Show a list of unique town names for all buildings in the Queensland region:
SELECT DISTINCT a.name
FROM building a, region b
WHERE st_within(a.the_geom, b.the_geom)
WHERE st_within(a.geom, b.geom)
AND b.name = 'Queensland';
Result:
Expand All @@ -317,48 +317,48 @@ Further examples ...
CREATE VIEW vw_shortestline AS
SELECT b.gid AS gid,
ST_ASTEXT(ST_SHORTESTLINE(a.the_geom, b.the_geom)) as text,
ST_SHORTESTLINE(a.the_geom, b.the_geom) AS the_geom
ST_ASTEXT(ST_SHORTESTLINE(a.geom, b.geom)) as text,
ST_SHORTESTLINE(a.geom, b.geom) AS geom
FROM road a, building b
WHERE a.id=5 AND b.id=22;
CREATE VIEW vw_longestline AS
SELECT b.gid AS gid,
ST_ASTEXT(ST_LONGESTLINE(a.the_geom, b.the_geom)) as text,
ST_LONGESTLINE(a.the_geom, b.the_geom) AS the_geom
ST_ASTEXT(ST_LONGESTLINE(a.geom, b.geom)) as text,
ST_LONGESTLINE(a.geom, b.geom) AS geom
FROM road a, building b
WHERE a.id=5 AND b.id=22;
.. code-block:: sql
CREATE VIEW vw_road_centroid AS
SELECT a.gid as gid, ST_CENTROID(a.the_geom) as the_geom
SELECT a.gid as gid, ST_CENTROID(a.geom) as geom
FROM road a
WHERE a.id = 1;
CREATE VIEW vw_region_centroid AS
SELECT a.gid as gid, ST_CENTROID(a.the_geom) as the_geom
SELECT a.gid as gid, ST_CENTROID(a.geom) as geom
FROM region a
WHERE a.name = 'Saskatchewan';
.. code-block:: sql
SELECT ST_PERIMETER(a.the_geom)
SELECT ST_PERIMETER(a.geom)
FROM region a
WHERE a.name='Queensland';
SELECT ST_AREA(a.the_geom)
SELECT ST_AREA(a.geom)
FROM region a
WHERE a.name='Queensland';
.. code-block:: sql
CREATE VIEW vw_simplify AS
SELECT gid, ST_Simplify(the_geom, 20) AS the_geom
SELECT gid, ST_Simplify(geom, 20) AS geom
FROM road;
CREATE VIEW vw_simplify_more AS
SELECT gid, ST_Simplify(the_geom, 50) AS the_geom
SELECT gid, ST_Simplify(geom, 50) AS geom
FROM road;
.. code-block:: sql
Expand All @@ -367,7 +367,7 @@ Further examples ...
SELECT
ROW_NUMBER() over (order by a.name) as id,
a.name as town,
ST_CONVEXHULL(ST_COLLECT(a.the_geom)) AS the_geom
ST_CONVEXHULL(ST_COLLECT(a.geom)) AS geom
FROM building a
GROUP BY a.name;
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