title: Oracle SQL - JOIN table on itself, ON (column * -1)
body: <p>I have a table <code>A</code> like</p>
  
  <pre><code>ID NAME AMOUNT, AGE, COMMENT
  1  Fred  10     11   likes ice cream
  2  Joe   20     12   hates ice cream
  3  Mike  -10    44   missing
  </code></pre>
  
  <p>I'd like to have the result set by inner joining on itself on A.AMOUNT equal to -1 * B.AMOUNT:</p>
  
  <pre><code>ID NAME AMOUNT, AGE, COMMENT          B.AMOUNT    B.COMMENT2
  1  Fred  10     11   likes ice cream   -10         missing
  </code></pre>
  
  <p>I've tried <code>A.AMOUNT = -B.AMOUNT, 
  A.AMOUNT = -1*B.AMOUNT, 
  CONCAT('-',B.AMOUNT) = A.AMOUNT</code></p>
  
  <p>But none of them seem to work. With <code>CONCAT</code>, I get <code>ORA-01722: invalid number</code></p>