isnull on an aggregate expression does not work

[1600eads]

Happy New Year! Want to say thanks to you all in this forum. Have been tremendous on helping me get up to speed. 

I have a particular issue with trying to use an if statement to display a simple 'PENDING' and/or 'COMPLETE' text. 

Here is an overview of the data:

There is a process of when an ID is PENDING and COMPLETE. I was helped before with finding the difference in days that stems from the same DATE column (column B). I don't think you can use a mixture of ifs and aggr syntaxes within the script so I tried to run it on the front end charts but was running into issues. Ultimately, take example ID# 5,6,7,10 - they were once PENDING then COMPLETE. Once that was initiated, I was able to find the difference in days. What I would like my output to be is COMPLETE instead of PENDING and COMPLETE as seen on column C since these orders are now complete.

This is where I tried to use the if statement: 

if(STATUS='PENDING' AND not isnull(SALESPERSON) and isnull(Aggr(Interval(Only({<STATUS={'COMPLETE'}>} PROCESSED_TIMESTAMP)-Only({<STATUS={'PENDING'}>} UPDATED_DATE), 'D'), ID) ) ,'PENDING',
if(STATUS='COMPLETE','COMPLETE')) 

To summarize - if the status is pending and a salesperson has been tied to that order and if there are no days difference then we know that process is still in the works/pending. if the status has both rows of the status PENDING and COMPLETE and also has a value for the daysdiff then we know that order has been complete. 

Looking for further directions and guidance if anyone has any! Thanks again.

[1600eads]

I was able to figure out my issue. For simplicity sake I will be using the same expression, but how does one use an aggregate function to create a flag dimension on the script level?

I'd like to create a flag dimension for this expression:

if(STATUS='PENDING' AND not isnull(SALESPERSON) and isnull(Aggr(Interval(Only({<STATUS={'COMPLETE'}>} PROCESSED_TIMESTAMP)-Only({<STATUS={'PENDING'}>} UPDATED_DATE), 'D'), ID) ) ,'PENDING',
if(STATUS='COMPLETE','COMPLETE')) 

Thanks again.