title: MySQL AUTO DECREMENT instead of AUTO INCREMENT, is it possible?
body: <p>I would like to have negative auto generated keys on a table.</p>
  
  <p>Instead of Keys: 1,2,3,..,X
  I would like Keys: -1,-2,-3,...,-X</p>
  
  <p>I need this because I have to create a mirror table to use in UNION with the original and 'understand' which records come from the original table and which ones come from the mirror table.</p>
  
  <p>Do you think this is a good idea?
  Is there a simple way to get negative auto decremented key? Or do I have to use triggers?</p>