select *  from emp
    where contains(ename,'MILLER')>0 and rownum < 10;
    
ORA-00904: "CONTAINS": invalid identifier
00904. 00000 -  "%s: invalid identifier"
*Cause:    
*Action:
Error at Line: 2 Column: 11

SQL> CREATE INDEX idxName ON emp(ename) INDEXTYPE IS CTXSYS.CONTEXT
  2  /
Index created

SQL> select *  from emp where contains(ename,'MILLER')>0 and rownum < 2
  2  /

EMPNO ENAME      JOB         MGR HIREDATE          SAL      COMM DEPTNO
----- ---------- --------- ----- ----------- --------- --------- ------
 7934 MILLER     CLERK      7782 1/23/1982     1300.00               10

SQL> drop index idxname;
Index dropped

SQL> select *  from emp where contains(ename,'MILLER')>0 and rownum < 2;
select *  from emp where contains(ename,'MILLER')>0 and rownum < 2
*
ERROR at line 1:
ORA-20000: Oracle Text error:
DRG-10599: column is not indexed

SQL> @$ORAC1020.ctx.admin.catctx.sql CTXSYS SYSAUX TEMP NOLOCK;
SP2-0310: unable to open file "$ORAC1020.ctx.admin.catctx.sql"
SQL>

select *  from DEPT where contains(DNAME,'ACCOUNTING')>0 and rownum < 2;

ORA-20000: Oracle Text error:
DRG-10599: column is not indexed
20000. 00000 -  "%s"
*Cause:    The stored procedure 'raise_application_error'
           was called which causes this error to be generated.
*Action:   Correct the problem as described in the error message or contact
           the application administrator or DBA for more information.

     
CREATE INDEX idxNamee ON DEPT(DNAME) INDEXTYPE IS CTXSYS.CONTEXT;

Error starting at line : 73 in command -
CREATE INDEX idxNamee ON DEPT(DNAME) INDEXTYPE IS CTXSYS.CONTEXT
Error at Command Line : 73 Column : 14
Error report -
SQL Error: ORA-29855: error occurred in the execution of ODCIINDEXCREATE routine
ORA-20000: Oracle Text error:
DRG-10700: preference does not exist: CTXSYS.DEFAULT_LEXER
ORA-06512: at "CTXSYS.DRUE", line 160
ORA-06512: at "CTXSYS.TEXTINDEXMETHODS", line 364
29855. 00000 -  "error occurred in the execution of ODCIINDEXCREATE routine"
*Cause:    Failed to successfully execute the ODCIIndexCreate routine.
*Action:   Check to see if the routine has been coded correctly.

SELECT  PRE_OWNER,
        PRE_NAME
  FROM  CTXSYS.CTX_PREFERENCES
  WHERE PRE_NAME = 'DEFAULT_LEXER';

SQL> show user
USER is "SYS"
SQL> SELECT  PRE_OWNER,
        PRE_NAME
  FROM  CTXSYS.CTX_PREFERENCES
  WHERE PRE_NAME = 'DEFAULT_LEXER';  2    3    4

no rows selected

SQL>

select  comp_name,
        status,
        version
  from  dba_registry
  where comp_id = 'CONTEXT'
/