support GROUP BY ALL in BigQuery

[bmagyarkuti]

Add support for BigQuery's GROUP BY ALL (documentation, release notes).

I've checked, and just allowing keyword ALL would have been enough as well (there was no need to introduce a new group_by_all type). I introduced the new group_by_all type because I felt it was preferrable to be explicit, rather than relying on a solution that "worked by accident", but I'm a little hesitant about this. If you'd prefer the simple solution, feel free to use that instead.

In addition, I also considered a separate GROUP BY ALL clause, which would have disallowed mixing GROUP BY ALL with elements from other syntax variants. I decided against this because you wrote you didn't intend this to be an SQL validator.

[nene]

Thanks a lot.

This is somewhat confusing case as it looks super similar to the GROUP BY [ALL | DISTINCT] expr syntax supported by PostgreSQL, but it really has a completely different meaning.

I think your solution is perfect.

[bmagyarkuti]

Thanks for the quick review!