Warning on column dupliactes #24
Description
With SQL it's possible to query the same Column-alias within a single SQL query. Then, the exercises app will overwrite one columns with the other, as they share the same key in the SqlResult data model. This can be really bad, as the actual SQL result returned by the database differs and will cause CREATE statements based on these selects to fail without any obvious reason for the user.
Either implement a warning, if there are duplicates, or suffix the columns like _1 etc. Or both.