>Despite someone says that this is not documented,
>I don't believe someone succeeds in finding an against example.

One example I could quote to you would be that previous version of VFP allowed to include fields in the dields list that were not aggregates nor part of the group by. This was a quirk of VFP and not part of standard SQL syntax. Suddenly one day they fixed it and then a whole bunch of code had to revisited.

It is a bad idea to depend on a sideeffect of a specific implementation of SQL. Your code is then NOT portable to other SQL environments like SQL Server or Oracle.