UPDATEMODE=

MISSINGCHECK
prevents missing values in transaction data set from replacing values in master data set.

NOMISSINGCHECK
allows missing values in transaction data set to replace values in master data set.

/*create or update permanent dataset based on their exsistence*/
%macro update;
proc sort data=trans; by store; run;

%if %sysfunc(exist(ABC.master))=0 %then %do;
data ABC.master;
set trans;
run;
%end;

%else %do;
data ABC.master;
update ABC.master trans UPDATEMODE=NOMISSINGCHECK;
by store;
run;
%end;

%mend;
%update;