title: Updating table's rows with operations between two tables
body: <p>I am trying to make a query to avoid having to use too much php. I would like to update <strong>world1</strong>'s rows (wood, wheat, gold, meat) by adding to these values the values of the table <strong>upgrading</strong>. This is as far as I could get :</p>
  
  <pre><code>SELECT wood_cancel, wheat_cancel, gold_cancel, meat_cancel FROM upgrading WHERE world = 'world1' AND player_id = 190 AND city_id = 1 AND cancel_id = 'cancel_wood_rate_1';
  UPDATE world1 SET wood = wood + wood_cancel, wheat = wheat + wheat_cancel, gold = gold + gold_cancel, meat = meat + meat_cancel WHERE player_id = 190 AND city_id = 1;
  DELETE FROM upgrading WHERE world = 'world1' AND player_id = 190 AND city_id = 1 AND cancel_id = 'cancel_wood_rate_1'SELECT wood_cancel, wheat_cancel, gold_cancel, meat_cancel FROM upgrading WHERE world = 'world1' AND player_id = 190 AND city_id = 1 AND cancel_id = 'cancel_wood_rate_1';
  </code></pre>
  
  <p>The SQL error message says  wood_cancel, wheat_cancel, gold_cancel and meat_cancel can't be found. How should I proceed ?</p>
  
  <p>Do I need to use some kind of JOIN ? If so, how ?</p>