Help With Extracting a SUM from the database

I want to use the sum of some values from the database.

I have this query called booking_allocations:

sum1001023×541 75.7 KB

Which I assumed would return the sum of the fields found. However it is only returning single field value:

sum101778×211 35.5 KB

What do I need to do in order to return the sum, so for example to return
amount_allocated_local_sum = 360.00…?

And how do I then access that value in a Set Value?