Unnesting not happening, But unnest hint is working, here is the current , Version 12.1.0.2.0.

Unnesting not happening, But unnest hint is working,  here is the current , Version 12.1.0.2.0.

_unnest_subquery                              TRUE 

_optimizer_unnest_all_subqueries              TRUE 

_optimizer_unnest_scalar_sq                   TRUE 

_distinct_view_unnesting                      FALSE

_optimizer_squ_bottomup                       TRUE 

_optimizer_unnest_disjunctive_subq            TRUE 

_optimizer_unnest_corr_set_subq               TRUE 

_optimizer_push_pred_cost_based     TRUE