进入sqlplus后，不使用set语句进行设置，默认格式：
SQL> select * from jobs;
JOB_ID JOB_TITLE MIN_SALARY MAX_SALARY #这行是head
---------- ----------------------------------- ---------- ----------
AD_PRES President 20080
40000
AD_VP Administration Vice President 15000 30000
AD_ASST Administration Assistant 3000 6000
FI_MGR Finance Manager 8200 16000
FI_ACCOUNT Accountant 4200 9000
AC_MGR Accounting Manager 8200 16000
AC_ACCOUNT Public Accountant 4200
