While dropping an index,all the constraints cascaded to that index should be either disabled or dropped
SQL> !oerr ora 02429
02429, 00000, "cannot drop index used for enforcement of unique/primary key"
// *Cause: user attempted to drop an index that is being used as the
// enforcement mechanism for unique or primary key.
// *Action: drop the constraint instead of the index.
Solution:
Check the constraints related to that index
SQL> select constraint_name from dba_constraints where table_name in ('T','S');
CONSTRAINT_NAME
--------------------------------------------------------------------------------
PK_T
FK_T
PK_S
Primary key and foreign key for the table is disabled and respective index is wiped!
SQL> alter table t disable constraint FK_T;
Table altered.
SQL> alter table s disable constraint PK_S;
Table altered.
