What about something like this to get the sum of an individual tile?
Code:
PARAMETERS x_param Long, y_param Long;
SELECT (SELECT Sum(some_table.n) AS expr01
FROM some_table
WHERE ( ( ( some_table.x ) Between [x_param] - 1 And [x_param] + 1 )
AND ( ( some_table.y ) Between [y_param] - 1 And [y_param] + 1
) ))
- n AS n_sum
FROM some_table
WHERE x = x_param
and y = y_param;
Or something like this to sum all the tiles
Code:
SELECT (SELECT Sum(sq.n) AS n_sum FROM some_table AS sq
WHERE ( ( ( sq.x ) Between q.x - 1 And q.x + 1 )
AND ( ( sq.y ) Between q.y - 1 And q.y + 1 ) )) - q.n AS n_sum
FROM some_table AS q