Oracle常用的函数:
sysdate
systimestamp
to_char 
to_date:
select to_date('06-5月-1957','DD-Mon-YY') from dual;
nvl:
select nvl(sal,'空') from emp;
decode:
decode(条件,值1,翻译值1,值2,翻译值2,...值n,翻译值n,缺省值)
该函数的含义如下:
IF 条件=值1 THEN
    RETURN(翻译值1)
ELSIF 条件=值2 THEN
    RETURN(翻译值2)
    ......
ELSIF 条件=值n THEN
    RETURN(翻译值n)
ELSE
    RETURN(缺省值)
END IF
String sql =
        "select product_name,sum(decode(bill_month,'"+chargePeriod+"',charge))/100 as cur_charge,
sum(decode(bill_month,'"+lastPeriod+"',charge))/100 as last_charge, "
        +
        " sum(decode(bill_month,'"+chargePeriod+"',bill_time_len))/60 as cur_time,
sum(decode(bill_month,'"+lastPeriod+"',bill_time_len))/60 as last_time "
        +
        " from tl_acc_report "
        +
        " group by product_name ";
SELECT sid,serial#,username,
DECODE(command
,0,’None’
,2,’Insert’
,3,’Select’
,6,’Update’
,7,’Delete’
,8,’Drop
,’Other’) cmd from des