title: how to do minus in string sql
body: <p>I've the column on the table like FurnaceRunno (GM15-737). So, I want to do minus one in FurnaceRunno.</p>
  
  <p>the output should come like this:(minus one value, fixed for every furnacerunno)</p>
  
  <pre><code>FurnaceRunno  :GM15-737      
  output        :GM15-736  
  </code></pre>