How does Oracle know if the an index was created by the PK constraint or the index was pre-created

  If the index was created via a PK constraint Oracle knows that it is coupled and both are dropped when the
PK constraint is dropped.  If they're not coupled (index pre-created), only the constraint is dropped and the index is
left in place.

 

Which SYS view will give this information? Oracle somehow knows it.

 

In my tests the information in DBA_INDEXES and DBA_CONSTRAINTS are identical whether the index was created by the PK constraint or the index was pre-created

Thanks