SQL> col dt noprint
SQL> select hiredate dt, to_char(hiredate,'DD/MM/YYYY') hiredate, ename from emp order by dt;
HIREDATE   ENAME
---------- ----------
17/12/1980 SMITH
20/02/1981 ALLEN
22/02/1981 WARD
02/04/1981 JONES
01/05/1981 BLAKE
09/06/1981 CLARK
08/09/1981 TURNER
28/09/1981 MARTIN
17/11/1981 KING
03/12/1981 JAMES
03/12/1981 FORD
23/01/1982 MILLER
19/04/1987 SCOTT
23/05/1987 ADAMS

where sqlplus

SQL> help reserved

 RESERVED WORDS (PL/SQL)
 -----------------------

 PL/SQL Reserved Words have special meaning in PL/SQL, and may not be used
 for identifier names (unless enclosed in "quotes").

 An asterisk (*) indicates words are also SQL Reserved Words.

 ALL*            DESC*           JAVA            PACKAGE         SUBTYPE
 ALTER*          DISTINCT*       LEVEL*          PARTITION       SUCCESSFUL*
 AND*            DO              LIKE*           PCTFREE*        SUM
 ANY*            DROP*           LIMITED         PLS_INTEGER     SYNONYM*
 ARRAY           ELSE*           LOCK*           POSITIVE        SYSDATE*
 AS*             ELSIF           LONG*           POSITIVEN       TABLE*
 ASC*            END             LOOP            PRAGMA          THEN*
 AT              EXCEPTION       MAX             PRIOR*          TIME
 AUTHID          EXCLUSIVE*      MIN             PRIVATE         TIMESTAMP
 AVG             EXECUTE         MINUS*          PROCEDURE       TIMEZONE_ABBR
 BEGIN           EXISTS*         MINUTE          PUBLIC*         TIMEZONE_HOUR
 BETWEEN*        EXIT            MLSLABEL*       RAISE           TIMEZONE_MINUTE

 BINARY_INTEGER  EXTENDS         MOD             RANGE           TIMEZONE_REGION

 BODY            EXTRACT         MODE*           RAW*            TO*
 BOOLEAN         FALSE           MONTH           REAL            TRIGGER*
 BULK            FETCH           NATURAL         RECORD          TRUE
 BY*             FLOAT*          NATURALN        REF             TYPE
 CHAR*           FOR*            NEW             RELEASE         UI
 CHAR_BASE       FORALL          NEXTVAL         RETURN          UNION*
 CHECK*          FROM*           NOCOPY          REVERSE         UNIQUE*
 CLOSE           FUNCTION        NOT*            ROLLBACK        UPDATE*
 CLUSTER*        GOTO            NOWAIT*         ROW*            USE
 COALESCE        GROUP*          NULL*           ROWID*          USER*
 COLLECT         HAVING*         NULLIF          ROWNUM*         VALIDATE*
 COMMENT*        HEAP            NUMBER*         ROWTYPE         VALUES*
 COMMIT          HOUR            NUMBER_BASE     SAVEPOINT       VARCHAR*
 COMPRESS*       IF              OCIROWID        SECOND          VARCHAR2*
 CONNECT*        IMMEDIATE*      OF*             SELECT*         VARIANCE
 CONSTANT        IN*             ON*             SEPERATE        VIEW*
 CREATE*         INDEX*          OPAQUE          SET*            WHEN
 CURRENT*        INDICATOR       OPEN            SHARE*          WHENEVER*
 CURRVAL         INSERT*         OPERATOR        SMALLINT*       WHERE*
 CURSOR          INTEGER*        OPTION*         SPACE           WHILE
 DATE*           INTERFACE       OR*             SQL             WITH*
 DAY             INTERSECT*      ORDER*          SQLCODE         WORK
 DECIMAL*        INTERVAL        ORGANIZATION    SQLERRM         WRITE
 DECLARE         INTO*           OTHERS          START*          YEAR
 DEFAULT*        IS*             OUT             STDDEV          ZONE
 DELETE*         ISOLATION


 RESERVED WORDS (SQL)
 --------------------

 SQL Reserved Words have special meaning in SQL, and may not be used for
 identifier names unless enclosed in "quotes".

 An asterisk (*) indicates words are also ANSI Reserved Words.

 Oracle prefixes implicitly generated schema object and subobject names
 with "SYS_". To avoid name resolution conflict, Oracle discourages you
 from prefixing your schema object and subobject names with "SYS_".

 ACCESS          DEFAULT*         INTEGER*        ONLINE          START
 ADD*            DELETE*          INTERSECT*      OPTION*         SUCCESSFUL
 ALL*            DESC*            INTO*           OR*             SYNONYM
 ALTER*          DISTINCT*        IS*             ORDER*          SYSDATE
 AND*            DROP*            LEVEL*          PCTFREE         TABLE*
 ANY*            ELSE*            LIKE*           PRIOR*          THEN*
 AS*             EXCLUSIVE        LOCK            PRIVILEGES*     TO*
 ASC*            EXISTS           LONG            PUBLIC*         TRIGGER
 AUDIT           FILE             MAXEXTENTS      RAW             UID
 BETWEEN*        FLOAT*           MINUS           RENAME          UNION*
 BY*             FOR*             MLSLABEL        RESOURCE        UNIQUE*
 CHAR*           FROM*            MODE            REVOKE*         UPDATE*
 CHECK*          GRANT*           MODIFY          ROW             USER*
 CLUSTER         GROUP*           NOAUDIT         ROWID           VALIDATE
 COLUMN          HAVING*          NOCOMPRESS      ROWNUM          VALUES*
 COMMENT         IDENTIFIED       NOT*            ROWS*           VARCHAR*
 COMPRESS        IMMEDIATE*       NOWAIT          SELECT*         VARCHAR2
 CONNECT*        IN*              NULL*           SESSION*        VIEW*
 CREATE*         INCREMENT        NUMBER          SET*            WHENEVER*
 CURRENT*        INDEX            OF*             SHARE           WHERE
 DATE*           INITIAL          OFFLINE         SIZE*           WITH*
 DECIMAL*        INSERT*          ON*             SMALLINT*

~ $ echo $PATH
/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/pfk/app/oracle/product/11.2.0//bin:/pfk/bin:/home/oracle/bin
~ $ where sqlplus
-bash: where: command not found
~ $ which sqlplus
/pfk/app/oracle/product/11.2.0/bin/sqlplus

SET UNDERLINE OFF

SQL> SELECT empno, ename FROM emp WHERE ROWNUM <= 5;

     EMPNO ENAME
---------- ----------
      7369 SMITH
      7499 ALLEN
      7521 WARD
      7566 JONES
      7654 MARTIN

SQL> SET UNDERLINE OFF
SQL> SELECT empno, ename FROM emp WHERE ROWNUM <= 5;

     EMPNO ENAME
      7369 SMITH
      7499 ALLEN
      7521 WARD
      7566 JONES
      7654 MARTIN

SQL>