title: combine multiple columns into one
body: <p>I came up with this query - how do I combine results from multiple columns into 1 ?</p>
  
  <pre><code>select 
      R2.start_time,
      TIME_FORMAT(time(R2.start_time - time(10000)),
              '%H:%i:%s') as '-60min',
      TIME_FORMAT(time(R2.start_time - time(3000)),
              '%H:%i:%s') as '-30min',
      TIME_FORMAT(time(R2.start_time + time(10000)) - time(3000),
              '%H:%i:%s') as 30min,
      TIME_FORMAT(time(R2.start_time + time(10000)),
              '%H:%i:%s') as 60min
  from
      (select 
          rooms.id, rooms.number, rooms.building, rooms.capacity
      from
          rooms) R1,
      (select 
          exam_schedules.room_id,
              exam_schedules.day,
              exam_schedules.start_time,
              exam_schedules.end_time
      from
          exam_schedules) R2
  where
      R2.room_id = R1.id and R2.day = 'tuesday' AND R1.number = 006
  group by 1
  </code></pre>
  
  <p>this is my result:(1 row)</p>
  
  <pre><code>12:30:00    11:30:00    12:00:00    13:00:00    13:30:00
  </code></pre>
  
  <p>should be (5 rows):</p>
  
  <pre><code>12:30:00
  11:30:00
  12:00:00
  13:00:00
  13:30:00
  </code></pre>