Create in lookml a total measure that ignores dimensions

[Rub_moy]

Hi everyone, 
I need to create an measure in lookml that always shows the total value of a field (ie sum(total_amount)), regardless of whether you group by dimensions or not. Basically, I need something that does the same thing than the 'totals' while exploring data:

Is there any way to achieve that in lookml? 

Thanks in advance!