What is the "SYS_C00054_14031410:34:03$" column in my regular Oracle table?
Unused columns.

SQL&gt; create table t1 as select * from dba_roles;

Table created.

SQL&gt; desc t1
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ROLE                                      NOT NULL VARCHAR2(30)
 PASSWORD_REQUIRED                                  VARCHAR2(8)
 AUTHENTICATION_TYPE                                VARCHAR2(11)

SQL&gt; alter table t1 set unused (AUTHENTICATION_TYPE);

Table altered.

SQL&gt; desc t1
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ROLE                                      NOT NULL VARCHAR2(30)
 PASSWORD_REQUIRED                                  VARCHAR2(8)

SQL&gt; select column_name from user_tab_cols where table_name = 'T1';

COLUMN_NAME
------------------------------
SYS_C00003_18012517:25:39$
PASSWORD_REQUIRED
ROLE

SQL&gt; alter table t1 drop unused columns;

Table altered.

SQL&gt; select column_name from user_tab_cols where table_name = 'T1';

COLUMN_NAME
------------------------------
PASSWORD_REQUIRED
ROLE


Edit:

Extra information: I used *_TAB_COLS, because *_TAB_COLUMNS does not list such columns.