I wrote these macros to add, drop or rename fields. Each checks to see if the field already exists. For addfield, 4th parameter is length for character field or format for numeric field.
%macro AddField(ds, field, type, lenfmt);
%local rc dsid result resx;
%let dsid = %sysfunc(open(&ds));
%let resx = %sysfunc(varnum(&dsid, &field));
%let rc = %sysfunc(close(&dsid));
%if %upcase(&type)=C %then %let spec=char(&lenfmt); %else %let spec=num;
/*%LET FIND_period = %INDEX(&lenfmt,%str(.)) ;
%IF %upcase(&type)=N and %eval(&FIND_period) = 0 %THEN %LET lenfmt= &lenfmt.%str(.);*/
%if %upcase(&type)=N and %length(&lenfmt)>1 %then %let lenfmt=%str(format=)&lenfmt; %else %let lenfmt=;
%if &resx > 0 %then %do;
%let result = 1;
%put NOTE: field &field already exists in &ds;
%end;
%else %do;
%let result = 0;
%put NOTE: field &field does not exist in &ds and will be added;
proc sql;
alter table &ds
add &field &spec &lenfmt
;
quit;
%end;
%mend AddField;
/* ********************************************************************** */
%macro DropField(ds, field);
%local rc dsid result resx;
%let dsid = %sysfunc(open(&ds));
%let resx = %sysfunc(varnum(&dsid, &field));
%let rc = %sysfunc(close(&dsid));
%if &resx > 0 %then %do;
%let result = 1;
%put NOTE: field &field exists in &ds and will be dropped;
proc sql;
alter table &ds
drop &field ;
quit;
%end;
%else %do;
%let result = 0;
%put NOTE: field &field does not exist in &ds;
%end;
%mend DropField;
/* ********************************************************************** */
%macro RenameField(ds, field, newname);
%local rc dsid result resx;
%let dsid = %sysfunc(open(&ds));
%let resx = %sysfunc(varnum(&dsid, &field));
%let rc = %sysfunc(close(&dsid));
%if &resx > 0 %then %do;
%let result = 1;
%put NOTE: field &field exists in &ds and will be renamed to &newname ;
data &ds;
set &ds;
/*&newname = &field ;
drop &field ; */
rename &field = &newname ;
run;
%end;
%else %do;
%let result = 0;
%put NOTE: field &field does not exist in &ds;
%end;
%mend RenameField;
