The _optimizer_group_by_placement parameter is related to
s 11g bug (184.108.40.206.)
This is from MOSC Note. 8945586.8 - Wrong results using
GROUP BY placement where wrong results can occur when using
GROUP BY placement where the aggregate column gets pruned
from select list.
This is caused when required
aggregate columns are missing in the plan in the projection
list of operations.
Workaround is to set set
_optimizer_extend_jppd_view_types tips related to 11g r2