The _N_ condition is only in effect with the first observation. You will need to use a sorted input file and use a BY statement with the key variables, and retain the important variable(s) using the IF FIRST. THEN ; condition.
Check the SAS support http://support.sas.com/ website for DATA STEP PROGRAMMING discussion and using a BY statement and the FIRST. and LAST. conditions for additional details.
data latest( keep= client sku volume ) ;
* assuming the name of the raw data is CLIENTS ;
set clients( obs= 0 ) ; * getting column definitions ;
do while( not finished ) ;
set clients( rename= ( client= rawC )) end= finished ;
client = coalesce( rawC, client ) ;
if column CLIENT is character, use function COALESCEC() rather than COALESCE()
Message was edited by: Peter.C
getting column definitions was intended as comment, prefix with *
If willing to solve the problem (regardless of your focus/perspective), you will need to explain what code you attempted and exactly what error occurred or further explain "getting column definitions - Sas did not recognized. I couldn't make it work".