文档介绍：Forpersonaluseonlyinstudyandresearch;mercialuse  TO_DATE格式(以时间:2007-11-02  13:45:25为例)         Year:            yytwodigits两位年               显示值:07       yyythreedigits三位年               显示值:007       yyyyfourdigits四位年               显示值:2007                  Month:            mm   number    两位月             显示值:11       mon   abbreviated字符集表示         显示值:11月,若是英文版,显示nov           monthspelledout字符集表示         显示值:11月,若是英文版,显示november                Day:            dd   number        当月第几天       显示值:02       ddd   number        当年第几天       显示值:02       dy   abbreviated当周第几天简写   显示值:星期五,若是英文版,显示fri       day   spelledout  当周第几天全写   显示值:星期五,若是英文版,显示friday              ddspthspelledout,ordinaltwelfth                         Hour:             hh   twodigits12小时进制           显示值:01             hh24twodigits24小时进制           显示值:13                          Minute:             mi   twodigits60进制               显示值:45                          Second:             ss   twodigits60进制               显示值:25                          其它             Q    digit        季度                 显示值:4             WW   digit        当年第几周           显示值:44             W   digit         当月第几周           显示值:1                    24小时格式下时间范围为:0:00:00-23:59:59....            12小时格式下时间范围为:1:00:00-12:59:59....           (to_date,to_char)        selectto_char(sysdate,'yyyy-mm-ddhh24:mi:ss')asnowTimefromdual;  //日期转化为字符串  selectto_char(sysdate,'yyyy')asnowYear  fromdual;  //获取时间的年  selectto_char(sysdate,'mm')   asnowMonthfromdual;  //获取时间的月  selectto_char(sysdate,'dd')   asnowDay   fromdual;  //获取时间的日  selectto_char(sysdate,'hh24')asnowHour  fromdual;  //获取时间的时  selectto_char(sysdate,'mi')   asnowMinutefromdual;  //获取时间的分  selectto_char(sysdate,'ss')   asnowSecondfromdual;  //获取时间的秒   selectto_date('2004-05-0713:23:44','yyyy-mm-ddhh24:mi:ss')   fromdual//2.        selectto_char(to_date(222,'J'),'Jsp')fromdual           显示TwoHundredTwenty-Two           selectto_char(to_date('2002-08-26','yy