SQL> describe cop_profile_fields_data;
 Name                                                                          Null?    Type
 ----------------------------------------------------------------------------- -------- ----------------------------------------------------
 USER_ID                                                                       NOT NULL NUMBER(8)
 pf_institution                                                                         VARCHAR2(255)
 pf_inst                                                                                VARCHAR2(255)
 pf_in                                                                                  VARCHAR2(255)

SQL> alter table cop_profile_fields_data drop column pf_in;
alter table cop_profile_fields_data drop column pf_in
                                                *
ERROR at line 1:
ORA-00904: "PF_IN": invalid identifier