title: mysql convert float to double
body: <p>It is necessary to change the type of a table field (with data).
  From Float type to Double type.
  The code that does this:</p>
  
  <pre><code>ALTER TABLE `my_table`
  CHANGE COLUMN `my_value` `my_value` 
  DOUBLE NULL DEFAULT NULL AFTER `id`;
  </code></pre>
  
  <p>But I got a problem:
  All fractional numbers soured:
  Old value -> New value: </p>
  
  <pre><code>129.8 -&gt; 129.8000030517578
  117.9 -&gt; 117.9000015258789
  99.2 -&gt; 99.19999694824219
  </code></pre>
  
  <p>How to change the field type without data corruption?</p>