what is the best way to create a variable and keep it as missing

[alexdsa]

I need help in:

I need to create a variable - and keep it as missing as it is not present in my dataset. However to make it standard and if that variable comes back in future. 

Now i am using in the data step.

data inc;

     set sashelp.class;

      mhelp=" ";

run;

But in the above case if my mhelp variable comes back in future then it makes it as missing which i do not want to.

Any help

[RW9 · Accepted solution]

Create a template dataset which is what you want to be present, then set that with the data you get, best of both worlds:

proc sql;
  create table TEMPLATE (var1 char(200),var2 num,var3 char(50));
quit;

data data_in;
  var1="Abc";
  var3="Def";
run;

data want;
  set template data_in;
run;