title: merger one row with null values to not null values of another row mysql
body: <p>I want to merge two rows into one.The below format is in the database.</p>
  
  <pre><code>+----+---------+-----------------------+-------------------------+
  | id |  appid  |        photo          |         signature       |
  +====+=========+=======================+=========================+
  | 1  | 10001   | 10001.photograph.jpg  |    NULL                 |
  | 2  | 10001   | NULL                  |    10001.signature.jpg  |
  +----+---------+-----------------------+-------------------------+
  </code></pre>
  
  <p>I want a mysql query so that i can fetch data like below,</p>
  
  <pre><code>  +--------+------------------------+-------------------------+
    | appid  |  photo                 |    signature            |
    +========+========================+=========================+
    |10001   | 10001.photograph.jpg   |   10001.signature.jpg   |
    +--------+------------------------+-------------------------+
  </code></pre>
  
  <p>Kindly suggest...</p>