title: Using +0 in order clause
body: <p>I have a column "available" which either returns "yes" or for instance "30 min". 
  To sort this table we have found out that this works as intended where "Yes" comes first, and the "30 min" comes after.<br>
  <code>order by   available + 0 asc</code> <br>
  Even though this works we do not know why we have to put +0 to the column. Can someone elaborate?</p>
  
  <p>Edit: This is an example on a query<br>Note that all where clauses are not here, and the if(x is null) is to return something if there is no result aka null value.</p>
  
  <pre><code>select distinct r.rname, if(b.stime is null, 'Yes', 'Yes') as available, r.mperson
  from Rooms r left outer join Bookings b using (rname)
  union all
  select b.rname, concat(minute(timediff(b.etime, '$sdate')), ' min') as available,      r.mperson
  from     Bookings b inner join Rooms r using(rname)
  order by    available + 0 asc, rname asc
  </code></pre>