title: Can I do hash merge by multiple keys in SAS
body: <p>I would like to hash merge in SAS using two keys;</p>
  
  <p>The variable names for the lookup dataset called link_id 8. and ref_date 8.;
  The variable names for the merged dataset called link_id 8. and drug_date 8.;</p>
  
  <p>The code I used is as following:</p>
  
  <pre><code>data elig_bene_pres;
     length link_id ref_date 8.;
     call missing(link_id,ref_date):
     if _N_=1 then do;
        declare hash elig_bene(dataset:"bene.elig_bene_uid");
        elig_bene.defineKey("link_id","ref_date");
        elig_bene.defineDone();
     end;
     set data;
     if elig_bene.find(key:Link_ID,key:drug_dt)=0 then output;
  run;
  </code></pre>
  
  <p>But it seems that it is not found by these two keys. I just want to know whether my method is doable.</p>
  
  <p>Thanks!</p>