如何在ssrs报表中从sql设置第一行值？

Question

I'm working on SSRS report.

There are two main fields CurrentMV and PreviousMV both are having there different formulas but I'm taking PreviousMV as a value of CurrentMV using =Previous(Sum(Fields!CurrentMV.Value))

Now How can I set 1st field only from sql and rest of other as it is coming from expression?

Because of I'm using Previous function 1st value is always coming null :(

I have the field in reporting proc which can give me the values but How can I set both 1st values as well as Previous function ?

Using Ian posts in answer But , I want to display only 1st field from Sum(Fields!PreviousMV.Value) and all preceding values by using Previous(Sum(Fields!CurrentMV.Value))

I tried like following and getting syntax error:

=First(Sum(Fields!PreviousMV.Value)) ,Previous(Sum(Fields!CurrentMV.Value)) 

Answer 1

You can explicitly check for NULL values:

=IIf(IsNothing(Previous(Sum(Fields!CurrentMV.Value)))
    , Sum(Fields!PreviousMV.Value)
    , Previous(Sum(Fields!CurrentMV.Value)))

Since there are no Previous groups for the first group, this will return NULL for the first group, and hence the above expression will work for you.

Here is a simple report that uses the expression.

Data:

Report:

The expression value is the one above.

Result:

You can see it's picking up the values as intended.