1. Errors
alter table DEPARTMENTS# drop constraint departments_pk;
ORA-02273: this unique/primary key is referenced by some foreign keys
2. Solutions
select * from all_constraints
where constraint_type='R' and r_constraint_name='DEPARTMENTS_PK';
alter table EMPLOYEES# drop constraint EMP_TO_DEPT_FK;
alter table JOB_HISTORY# drop constraint JOB_HIST_TO_DEPARTMENTS_FK;
alter table BINHTV.DEPARTMENTS# drop constraint departments_pk; --> OK
