GROUPBY's total_depth only ever added one Total line. In Excel a depth
of N adds a subtotal line for each group of the first N - 1 key columns
(after the group, or before it when the depth is negative) and labels
the last line "Grand Total"; a depth greater than the number of key
columns, or above 1 with field_relationship 1 (a flat table), is
#VALUE!. The subtotals aggregate the group's source rows, so AVERAGE and
COUNT subtotals are right too.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>