Selecting polygon id's if their centroid falls in another polygon using PostGIS?

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2
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I'm trying to select polygons which centroids fall in another polygon:



enter image description here



SELECT smaller_polygons.id
FROM big_polygon
LEFT JOIN big_polygon smaller_polygons
ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)


I expect 33,44 to be selected but I get id of the big polygon.



What am I doing wrong?






postgis







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  • 1




    Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
    – Kazuhito
    1 hour ago










  • INNER JOIN seems to work with correct FROM table etc.
    – BERA
    50 mins ago














up vote
2
down vote

favorite












I'm trying to select polygons which centroids fall in another polygon:



enter image description here



SELECT smaller_polygons.id
FROM big_polygon
LEFT JOIN big_polygon smaller_polygons
ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)


I expect 33,44 to be selected but I get id of the big polygon.



What am I doing wrong?






postgis







share|improve this question



















  • 1




    Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
    – Kazuhito
    1 hour ago










  • INNER JOIN seems to work with correct FROM table etc.
    – BERA
    50 mins ago












up vote
2
down vote

favorite









up vote
2
down vote

favorite











I'm trying to select polygons which centroids fall in another polygon:



enter image description here



SELECT smaller_polygons.id
FROM big_polygon
LEFT JOIN big_polygon smaller_polygons
ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)


I expect 33,44 to be selected but I get id of the big polygon.



What am I doing wrong?






postgis







share|improve this question















I'm trying to select polygons which centroids fall in another polygon:



enter image description here



SELECT smaller_polygons.id
FROM big_polygon
LEFT JOIN big_polygon smaller_polygons
ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)


I expect 33,44 to be selected but I get id of the big polygon.



What am I doing wrong?






postgis




postgis






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 1 hour ago









PolyGeo♦

52.1k1779235




52.1k1779235










asked 1 hour ago









BERA

12.4k51737




12.4k51737







  • 1




    Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
    – Kazuhito
    1 hour ago










  • INNER JOIN seems to work with correct FROM table etc.
    – BERA
    50 mins ago












  • 1




    Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
    – Kazuhito
    1 hour ago










  • INNER JOIN seems to work with correct FROM table etc.
    – BERA
    50 mins ago







1




1




Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
– Kazuhito
1 hour ago




Hi BERA, it seems LEFT JOIN limits the records to the ones provided by the big_polygon table. How about CROSS JOIN?
– Kazuhito
1 hour ago












INNER JOIN seems to work with correct FROM table etc.
– BERA
50 mins ago




INNER JOIN seems to work with correct FROM table etc.
– BERA
50 mins ago










1 Answer
1






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up vote
2
down vote













This seems to work:



SELECT 
 smaller_polygons.id
FROM smaller_polygons
INNER JOIN big_polygon
ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)





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    1 Answer
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    oldest

    votes








    up vote
    2
    down vote













    This seems to work:



    SELECT 
     smaller_polygons.id
    FROM smaller_polygons
    INNER JOIN big_polygon
    ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)





    share|improve this answer
























      up vote
      2
      down vote













      This seems to work:



      SELECT 
       smaller_polygons.id
      FROM smaller_polygons
      INNER JOIN big_polygon
      ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)





      share|improve this answer






















        up vote
        2
        down vote










        up vote
        2
        down vote









        This seems to work:



        SELECT 
         smaller_polygons.id
        FROM smaller_polygons
        INNER JOIN big_polygon
        ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)





        share|improve this answer












        This seems to work:



        SELECT 
         smaller_polygons.id
        FROM smaller_polygons
        INNER JOIN big_polygon
        ON ST_Within(ST_Centroid(smaller_polygons.wkb_geometry),big_polygon.wkb_geometry)






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 58 mins ago









        BERA

        12.4k51737




        12.4k51737



























             

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