有没有办法从 POSTGRESQL 中的 json 数组中提取坐标

Question

I have this column "region" that has the following jsonb value

{ "type": "FeatureCollection"
, "features": [{
      "type": "Feature"
    , "geometry": { 
        "type": "Polygon"
      , "coordinates": [[
          [-105.31219482421875, 39.37252570201878]
        , [-104.403076171875, 39.37252570201878]
        , [-104.403076171875, 40.195659093364654]
        , [-105.31219482421875, 40.195659093364654]
        , [-105.31219482421875, 39.37252570201878]
        ]]
      }
    , "properties": {}
    }]
}

I'm trying to figure out how to extract the coordinate values from this nested json

Answer 1

On recent versions of PostgreSQL, it is possible to use json path queries to reshape the data succinctly.

create table x (jsonb_data) as 
select jsonb '{"type": "FeatureCollection", "features": [{"type": "Feature", "geometry": {"type": "Polygon", "coordinates": [[[-105.31219482421875, 39.37252570201878], [-104.403076171875, 39.37252570201878], [-104.403076171875, 40.195659093364654], [-105.31219482421875, 40.195659093364654], [-105.31219482421875, 39.37252570201878]]]}, "properties": {}}]}' jsonb_data;

SELECT
  jsonb_data
, (coord ->> 0)::float coord0
, (coord ->> 1)::float coord1
FROM x
JOIN LATERAL jsonb_path_query(
    jsonb_data
  , '$.features[*].geometry.coordinates[*][*]') coord 
          ON TRUE

Not going into too much detail, here's a bit of background of the various more advanced bits in this query:

jsonb_path_query function was introduced in version 12

JOIN LATERAL... ON TRUE in this query evaluates the expression ... for each row, and the evaulated expression unnests queries the json & unnests the resulting array.

(coord ->> 0)::float extracts the first numeric value from each coordinate list and converts it to a postgresql float.