title: Using formula in Crystal Report with empty data
body: <p>I'm new at Crystal report.</p>
  
  <p>I have 2 column in different table like this: </p>
  
  <pre><code>banyak    peminjaman_banyak      
    2               1                 
    3               1          
    3               2          
    4                       
  </code></pre>
  
  <p>when i enter this code :</p>
  
  <pre><code>tonumber({list_komponen1.banyak})-tonumber(sum({peminjaman_alat1.peminjaman_banyak},{list_komponen1.nama_komponen}))
  </code></pre>
  
  <p>i get the result like this :</p>
  
  <pre><code>banyak    peminjaman_banyak     Total     
    2               1           1   
    3               1           2
    3               2           1  
  </code></pre>
  
  <p>I want to show data like this:</p>
  
  <pre><code>banyak    peminjaman_banyak     Total     
    2               1               1
    3               1               2
    3               2               5
    4                               4
  </code></pre>
  
  <p>how can i subtract these table, when one off them doesn't have any value?
  I hope you can understand what i mean.</p>