Yikes. That is a very confusing way to write a data step. Remember the macro processor (the macro pre-processor) finishes its work before the resulting text is passed onto SAS itself to interpret. So putting macro code, ,especially macro definitions, in the middle of a data step is just going to confuse the humans trying to read the code.
So let's first try to untangle that so we can see what type of data step you are trying to generate with that macro code. So I think you are trying to run something like this:
%macro bb(num);
%local n beg end mon;
%do n=0 %to #
%let beg=%sysfunc(putn(%sysfunc(intnx(month,%sysfunc(today()),-&n)),date9.));
%let end=%sysfunc(putn(%sysfunc(intnx(month,%sysfunc(today()),-&n,end)),date9.));
%let mon=%sysfunc(putn(%sysfunc(intnx(month,%sysfunc(today()),-&n)),yymmd.));
if begin_date le "&end"d and end_date ge "&beg"d then do;
mon="&mon";
output;
end;
%end;
%mend;
data b;
set a;
%bb(num=%sysfunc(intck(month,'01jan2022'd,%sysfunc(today()))))
run;
Which would be a lot easier without the macro code. Perhaps like this?
data b;
set a;
do offset=0 to intck('month',max(begin_date,'01JAN2022'd),min(end_date,today));
mon = put(intnx('month',max(begin_date,'01JAN2022'd),offset),mmddd7.);
output;
end;
drop offset;
run;
If you wanted to so something like that in SQL code then create the target months as a dataset and join the target months with the data.
data months;
do offset=0 to intck('month','01JAN2022'd,today());
begdt = intnx('month','01JAN2022'd,offset);
enddt = intnx('month','01JAN2022'd,offset,'end');
mon = put(begdt,yymmd7.);
output;
end;
run;
proc sql;
create table b as
select a.*,b.mon
from a inner join months b
on a.begin_date le b.enddt and a.end_date ge b.begdt
;
quit;
