我想从数据库中选择性别相同，年龄相差不超过2岁的病例与对照，我参考了论坛帖子https://bbs.pinggu.org/thread-2845169-1-1.html，自己的程序如下，但总是失败，却不知道问题出在哪里，恳请各位大侠指点迷津，不胜感激！
data match;
input id sex age case;
cards;
1 1 34 1
2 1 35 0
3 2 65 1
4 2 66 0
5 1 11 1
run;
data a1;
set match;
pp=sex; *性别匹配变量pp;
run;
data a_case a_control;set a1;
if case=1 then output a_case; *病例数据集a_case;
if case=0 then output a_control; *对照数据集a_control;
run;

%macro ss;
proc datasets lib=work;delete sample;run;*清除前次抽选样本，方便重复运行宏抽样程序;
proc sql noprint;
select count(*) into: num from a_case; *统计病例个数;
%do i=1 %to &num
%let k=%eval(&i-1);
proc sql noprint;
select id into: idx separated by ' ' from a_case;  *病例ID号 到宏idx;
%let xx=%scan(&idx,&i,' ') ;
data case&i;set a_case;
if id=&xx then call symput("pp_v",pp); *相同匹配条件pp;
if id=&xx then call symput("age_v",age); run; *范围匹配条件age;
data control&i;set a_control;
if pp="&pp_v" and abs(age-&age_v)<3; run; *生成符合匹配条件control样本;
proc surveyselect noprint data=control&i method=srs n=1 out=sample&i seed=1000;        *n=1 ,1：1匹配;
data a_control;set a_control sample&i; run;
proc sql noprint;
create table a_control as  select * from a_control  group by id having n(id)=1;        *剔除已选择control样本;
%end;
data sample;set sample:;run; *生成匹配样本库;
data hb;set a_case sample;run; *生成总库;
proc datasets lib=work;save a1 js a_case a_control sample hb; run; *清除过程文件;
%mend;
%ss;