title: Convert result of CASE Expression to a number in Oracle SQL
body: <p>I have the following <code>select</code> query. I want to <em>convert</em> it from <code>string</code> into a <code>number</code>. If I wrap a <code>TO_NUMBER</code> around the case expression, I get </p>
  
  <blockquote>
    <p>expression must have same datatype as corresponding expression</p>
  </blockquote>
  
  <p><strong>error</strong>.</p>
  
  <pre><code>SELECT CASE SUBSTR(GRADE, INSTR(GRADE, ' ') + 1) 
           WHEN 'Unspecified' THEN ' '
           ELSE SUBSTR(GRADE, INSTR(GRADE, ' ') + 1) 
         END as Final_Grade,
  </code></pre>
  
  <p>How can I get <code>Final_Grade</code> to be <code>numeric</code>?</p>
  
  <p>Thank you!</p>