It is not clear what kind of output you want?? A report?? A dataset?? What kind of data is this?
You say the dataset has the following variables or columns:
CODE AMOUNT SINGLE_RECORD_FLAG
Then you say you want to set the value of SINGLE_RECORD_FLAG -- what is the current value of that variable? How did it get into the dataset in the first place?? If all you want to do is create or change a variable value that sounds like a job for FIRST.byvar, or LAST.byvar processing or if you want a report for PROC FREQ or PROC MEANS.