H3_postgis

SELECT h3_lat_lng_to_cell(ST_SetSRID(ST_MakePoint(-122.4194, 37.7749), 4326), 9);

SELECT h3_cell_to_geometry('8928308280fffff');

SELECT h3_cell_to_geometry(neighbor)
FROM h3_grid_disk('8928308280fffff', 1) AS neighbor;

SELECT ST_Contains(h3_cell_to_geometry('8928308280fffff'),
                   ST_SetSRID(ST_MakePoint(-122.4194, 37.7749), 4326));

CREATE TABLE locations (
    id SERIAL PRIMARY KEY,
    name TEXT,
    geom GEOMETRY(Point, 4326),
    h3_index H3INDEX
);

INSERT INTO locations (name, geom, h3_index)
VALUES ('San Francisco', ST_SetSRID(ST_MakePoint(-122.4194, 37.7749), 4326),
        h3_lat_lng_to_cell(ST_SetSRID(ST_MakePoint(-122.4194, 37.7749), 4326), 9));

SELECT DISTINCT l.name
FROM locations l
CROSS JOIN LATERAL (
    SELECT h3_grid_disk(h3_lat_lng_to_cell(l.geom, 9), 1) AS nearby_cell
) disk
WHERE l.h3_index = disk.nearby_cell;