title: Update count in growing table using php in MySQL
body: <p>table sample :</p>
  
  <pre><code>+--------+--------+-------+
  | source | target | count |
  +--------+--------+-------+
  | cat    | dog    |  NULL |
  | dog    | cat    |  NULL |
  +--------+--------+-------+
  </code></pre>
  
  <p>MySQL code :</p>
  
  <pre><code>update test set count = count+1 where source ='dog' and target='cat';
  </code></pre>
  
  <p>the count columns must be <code>1</code> after execute this MySQL code, but it never works,
  shall we give an initial value to <code>count</code>? this table could grow up every second, so that I can't use <code>COUNT(*)</code> solve this question, any suggestion? </p>