SAS - proc sql for table update in a macro -

i have code tries update table in macro block using macro variables in sub-query. challenge have @ times of macro variables null, making code fail. how can set ignore when macro varible produces null value?

    %macro update_bucket; %let macro_fudge = %nrstr(%mend);  proc sql; %do i=1 %to &rows.;      %do j=1 %to &max_comb.;          %do k=1 %to &max_lgd_comb.;              %do l=1 %to &max_pd_comb.;                    %let x = _&&k.lgd&i.;                    %let y = _&&l.pd&i.;                          %if &x. ^=ltv %then %do;                           update sbbook_rb_a                         set riskbucket = (select risk_bucket portfolio_split_d b                                 a.businessgroup = b.portfolio                                 , a.product2 = b._&j.subport                                 , a.&&&x. >= b.min_lgd_driver_%left(&k.) /* @ times "a.&&&x." returns null value */                                  , a.&&&x. < b.max_lgd_driver_%left(&k.)                                 , a.&&&y. >= b.min_pd_driver_%left(&l.) /* @ times "a.&&&y." returns null value */                                   , a.&&&y. < b.max_pd_driver_%left(&l.)                                              , b.row_num = &i.                                 )                         riskbucket = '';                     %end;             %end;         %end;     %end; %end; quit; %mend; %update_bucket; 

thank you

best practice in cases use parameters, not global macro variables. in case can give them default value, can test , skip loop (for example, give default value of 0).

%macro mymacro(param1=0, param2=0);  ... %mend mymacro; 

you should never rely on globals way did in code, regardless of this; macro variable used in macro should parameter macro, excepting global things paths (and then, prefer parameters). can pass global value parameter, should passed.