title: Concat two table columns and update one with result
body: <p>I have table that has two columns and I need to concatenate these two and update first column with result.<br>
  For example assume this is my table:  </p>
  
  <pre><code>+----+-------+-------+
  | id | col1  | col2  |
  +----+-------+-------+
  |  1 | text1 | text2 |
  +----+-------+-------+
  |  2 | text3 | text4 |
  +----+-------+-------+
  </code></pre>
  
  <p>after concatenation my table should be:  </p>
  
  <pre><code>+----+-------------+-------+
  | id |    col1     | col2  |
  +----+-------------+-------+
  |  1 | text1.text2 | text2 |
  +----+-------------+-------+
  |  2 | text3.text4 | text4 |
  +----+-------------+-------+
  </code></pre>
  
  <p>How can I do this using SQL?</p>