title: updating a column by a constant value
body: <p>I'm having difficulty with a simple issue.</p>
  
  <p>I have a number column a typical value is say 192.123.</p>
  
  <p>I want to add/subtract a single value to it, say -100.123.</p>
  
  <p>I assume it is</p>
  
  <pre><code>Update table_name
  SET column_name = (the original value - 100.123)
  </code></pre>
  
  <p>How should I go about this?</p>