aggregation first sorted values

[Lotteverhoeven]

Hi, I want to make a calculation based on the records in the appendix. 

What I want to do is I want to sum all the amounts in the column SUM_Production_SONO, but only the first record for the unique combination of the field Date, Order Number and Phase. 

I already tried formulas like:

Sum(
{<Measure={'Kilo'}>}
Aggr(
If(RowNo() = 1, Sum(Sum_Production_SONO), 0),
Date,
[Order Number],
Phase
)
)

AND

Sum(
{<Measure={'Kilo'}>}
Aggr(
If(RowNo() = 1, Sum(Sum_Production_SONO)),
Date,
[Order Number],
Phase
)
)

But they still give the sum of all the values instead of only the first one. Can someone help me with this?
Thank you in advance.

[marcus_sommer]

Maybe something like this:

if(Date = above(Date) and [Order Number] = above([Order Number]) and Phase = above(Phase),
   null(),
   Sum({<Measure={'Kilo'}>} Sum_Production_SONO))