title: Integrate separate year, month, day, hour, minute and second columns as a single timestamp column
body: <p>My data set contains separate year, month, day, hour, minute, and second columns as following that are separated by space:</p>
  
  <pre><code>+-------------------+
  |2007|09|28|21|14|06|
  |2007|09|28|21|14|06|
  |2007|09|28|21|14|06|
  |2007|09|28|21|14|06|
  |2007|09|28|21|14|06|
  +-------------------+
  </code></pre>
  
  <p>I wanted to integrate them as a single column under timestamp data-type.
  I have created a new column in timestamp data-type and update the column by following code:</p>
  
  <pre><code> Update s2
   set dt = year || '-' || month  || '-' || day
                 || ' ' || hour  || ':' || min  || ':' || second 
  </code></pre>
  
  <p>But I faced by following error:</p>
  
  <pre><code>ERROR:  column "dt" is of type timestamp without time zone but expression is of type text
  LINE 1:  Update temp set dt= year || '-' || month  || '-' || day  ||...
                               ^
  HINT:  You will need to rewrite or cast the expression.
  
  ********** Error **********
  
  ERROR: column "dt" is of type timestamp without time zone but expression is of type text
  SQL state: 42804
  Hint: You will need to rewrite or cast the expression.
  Character: 22
  </code></pre>
  
  <p>Moreover, I can preform the integration by <code>varchar</code> data-type.</p>