SELECT point.geometry AS geometry,
       grid.id AS id,
       grid.num AS num,
       st_distance(point.geometry, grid.geometry) AS dist
FROM point CROSS JOIN grid
ORDER BY st_distance(point.geometry, st_centroid(grid.geometry)) ASC

SELECT t1.geometry,
       t1.id AS id,
       t1.num AS num,
       t1.dist AS dist,
       sum(t2.num) AS cum
FROM temp t1 INNER JOIN temp t2
ON t1.dist >= t2.dist
GROUP BY t1.dist, t1.num
ORDER BY t1.dist, t1.num

SELECT grid.*
FROM grid INNER JOIN temp2
ON grid.id = temp2.id