title: UPDATE new_column instead of SELECT new_column
body: <p>I currently have this code:</p>
  
  <pre><code>SELECT x.id, x.company, x.dt, x.price, x.ctcy, (x.price - y.price)/y.price AS 'change'
  FROM 
  (
      SELECT a.id AS aid, MAX(b.id) AS aPrevid
      FROM price_practice a
      INNER JOIN price_practice b
      WHERE a.id &gt; b.id
      AND a.company = b.company
      GROUP BY a.id
  ) Sub1
  INNER JOIN price_practice x ON Sub1.aid = x.id
  INNER JOIN price_practice y ON Sub1.aPrevid = y.id
  ORDER BY x.id DESC
  </code></pre>
  
  <p>It returns:</p>
  
  <pre><code> id   company       dt       price  ctcy      change
  '35', 'Citi', '2015-07-14', '0.59', NULL, '-0.180556'
  '34', 'Citi', '2015-07-13', '0.72', NULL, '-0.088608'
  '33', 'Citi', '2015-07-10', '0.79', NULL, '-0.048193'
  '32', 'Citi', '2015-07-09', '0.83', NULL, '-0.126316'
  '31', 'Citi', '2015-07-08', '0.95', NULL, '-0.059406'
  '30', 'Amex', '2015-07-14', '6.01', NULL, '0.022109'
  '29', 'Amex', '2015-07-13', '5.88', NULL, '0.059459'
  '28', 'Amex', '2015-07-10', '5.55', NULL, '0.037383'
  '27', 'Amex', '2015-07-09', '5.35', NULL, '0.022945'
  '26', 'Amex', '2015-07-08', '5.23', NULL, '0.242280'
  '25', 'Citi', '2015-07-07', '1.01', NULL, '0.147727'
  '24', 'Citi', '2015-07-06', '0.88', NULL, '-0.120000'
  '23', 'Citi', '2015-07-03', '1.00', NULL, '-0.090909'
  '22', 'Citi', '2015-07-02', '1.10', NULL, '0.100000'
  '20', 'Amex', '2015-07-07', '4.21', NULL, '-0.284014'
  '19', 'Amex', '2015-07-06', '5.88', NULL, '0.176000'
  '18', 'Amex', '2015-07-03', '5.00', NULL, '-0.019608'
  '17', 'Amex', '2015-07-02', '5.10', NULL, '0.020000'
  </code></pre>
  
  <p>Rather than displaying the new data I calculate in the <code>change</code> column, I want to save it (<code>UPDATE</code>) in the the empty column <code>ctcy</code>. Not surprisingly replacing <code>SELECT</code> with <code>UPDATE</code> gives <code>Error Code: 1064</code> for line 1. So how do I do it?</p>