Reposting [my answer][1] to a similar question regarding SQL Server:

> In the SQL world, order is not an inherent property of a set of data.
> Thus, you get no guarantees from your RDBMS that your data will come
> back in a certain order -- or even in a consistent order -- unless you
> query your data with an ORDER BY clause.

So, to answer your question, MySQL sorts the records however it wants without any guarantee of consistency.

  [1]: http://dba.stackexchange.com/questions/5774/why-is-ssms-inserting-new-rows-at-the-top-of-a-table-not-the-bottom/5775#5775