Bigquery: Using ST_CLUSTERDBSCAN in an array of ST_GEOGPOINT

Question

I want to use ST_CLUSTERDBSCAN to cluster geopoints. The example in Bigquery page is this one:

WITH Geos as
  (SELECT 1 as row_id, st_geogfromtext('point empty') as geo UNION ALL
    SELECT 2, st_geogfromtext('multipoint(1 1, 2 2, 4 4, 5 2)') UNION ALL
    SELECT 3, st_geogfromtext('point(14 15)') UNION ALL
    SELECT 4, st_geogfromtext('linestring(40 1, 42 34, 44 39)') UNION ALL
    SELECT 5, st_geogfromtext('polygon((40 2, 40 1, 41 2, 40 2))'))
SELECT row_id, geo, ST_CLUSTERDBSCAN(geo, 1e5, 1) OVER () AS cluster_num FROM
Geos ORDER BY row_id
+--------+-----------------------------------+-------------+
| row_id |                geo                | cluster_num |
+--------+-----------------------------------+-------------+
|      1 |          GEOMETRYCOLLECTION EMPTY |        NULL |
|      2 |    MULTIPOINT(1 1, 2 2, 5 2, 4 4) |           0 |
|      3 |                      POINT(14 15) |           1 |
|      4 |    LINESTRING(40 1, 42 34, 44 39) |           2 |
|      5 | POLYGON((40 2, 40 1, 41 2, 40 2)) |           2 |
+--------+-----------------------------------+-------------+

In my code I have a Array of points that I aggregate together. However it seems to no work eventhout I see in the results as MULTIPOINT.

my code:

    ST_CLUSTERDBSCAN(ST_UNION_AGG(buyer_geo_point), 1e4, 2) OVER () AS cluster_num ,
    ST_UNION_AGG(buyer_geo_point)

The results are either null or have completely wrong values:

null
POINT(-41.5320687976469 -20.3600487114797)

null
MULTIPOINT(-39.0833794 -5.9597183, -39.00682744 -5.73228798)

null
POINT(-40.224447061747 -17.3677128083793)

null
POINT(-40.10711168 -18.08920528)
32  
null
POINT(-41.10854564 -21.47675214)

null
POINT(-51.11207578 -20.64520046)

117
MULTIPOINT(-38.08106136 -11.94490164, -38.06814822 -11.94196154)
    
117
MULTIPOINT(-38.07860266 -11.94484066, -38.0786308 -11.9448231, -38.0787098 -11.9447567, -38.0786912 -11.9447861, -38.0676091 -11.9453678)

null
MULTIPOINT(-39.98731268 -14.8426174, -39.98782804 -14.84623434)

UPDATE: I figure out a solution to have the points on each cluster labeled.

WITH  merchant_cluster as (SELECT  
        pl_gl.merchant_id, 
        ST_CLUSTERDBSCAN(buyer_geo_point, 1e3, 1) OVER (Partition by merchant_id) as clusters ,
        buyer_geo_point
    FROM `geo-info-table` as geo
    LEFT JOIN `merchants-table` as m on geo.merchant_id = m.user_id
    LEFT JOIN `adresses-table` as add on m.user_id = add.user_id
)
SELECT merchant_id, STRUCT(ARRAY_AGG(IFNULL(clusters,-1)) as cluster_id, ARRAY_AGG(buyer_geo_point) as point) FROM merchant_cluster 
GROUP BY merchant_id

Answer 1

Try below

select cluster_num, ST_UNION_AGG(buyer_geo_point) geo_cluster 
from (
  select buyer_geo_point,
    ST_CLUSTERDBSCAN(buyer_geo_point, 1e4, 2) OVER () AS cluster_num
  from `project.dataset.table`
)
group by cluster_num

I tried to mimic your data using points exposed in your question and got below result using above code (note - I used ST_CLUSTERDBSCAN(buyer_geo_point, 200000, 1) because of very small set of points)

Below is visualization of this result - each cluster assigned separate color