SQL中日期格式的处理to_char函数

1. 日期和字符转换函数用法（to_date,to_char）
   select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’) as nowTime from dual; //日期转化为字符串
   select to_char(sysdate,‘yyyy’) as nowYear from dual; //获取时间的年
   select to_char(sysdate,‘mm’) as nowMonth from dual; //获取时间的月
   select to_char(sysdate,‘dd’) as nowDay from dual; //获取时间的日
   select to_char(sysdate,‘hh24’) as nowHour from dual; //获取时间的时
   select to_char(sysdate,‘mi’) as nowMinute from dual; //获取时间的分
   select to_char(sysdate,‘ss’) as nowSecond from dual; //获取时间的秒

select to_date(‘2004-05-07 13:23:44’,‘yyyy-mm-dd hh24:mi:ss’) from dual//