How to get the system current time in Oracle ____oracle

How Oracle obtains system current time   Select To_char (sysdate, ' Yyyy-mm-dd hh24:mi:ss ') from dual;    Oracle gets a time of year, quarter, month, week , the function of the day   select  to_char (sysdate, ' yyyy ')  from dual; --year     Select  to_char (sysdate, ' MM ')  from dual; --month   Select  to_char (sysdate, ' DD ')  from dual; --Day   Select  to_char (sysdate, ' Q ')  from dual; --season   Select  to_char (sysdate, ' IW ')  from dual; --week--according to the calendar, there are 52 or 53 weeks per year  /*  hh hours (a)   hh24 hours (a)   Mi cent   SS sec   D Week of the day of the week of   DDD year &N Bsp The first weeks of the WW year   W the week of the month--January 1 to January 7 of the year is week one, and so on, 53 weeks a year   */      Get system date: Sysdate ()   format Date: &N Bsp      to_char (Sysdate (), ' Yy/mm/dd HH24:MI:SS)     or to_date (Sysdate (), ' Yy/mm/dd HH24:MI:SS ') & 　　 nbsp Select To_char (sysdate, ' yyyy-mm-dd HH24:mi:ss ')  from dual;  select To_char (sysdate, ' yyyy-mm-dd HH24:mm:ss ') )  from dual;  Select To_char (sysdate, 'Yy-mm-dd hh24:mi:ss ')  from dual  Select To_date (' 2009-12-25 14:23:31 ', ' Yyyy-mm-dd,hh24:mi:ss ') from DUAL&NB 　　Sp And if the upper-style writing:  select  to_date (' 2009-12-25 14:23:31 ', ' yyyy-mm-dd,hh:mi:ss ')  from dual  will be the error, because the hour HH is 12 binary, 14 is illegal input, cannot match.   Conversion Format:  represents the year's:      y for the last one,   yy to represent the last 2 digits of the year, the   yyy the last 3 digits of the year, and the   y YYY 4 digits for the year   month:      mm with 2-digit number for the month,   mon in shorthand form, such as November or Nov,   month with full name, such as November or 　　november  represents Day's:      DD for days of the month,   DDD indicates the days of the year,   dy Zhou Di days, such as Friday or Fri,   Day when Zhou Di a few days, full name, such as Friday or friday  hour:      HH 2 digits for hours 12,   hh24 2-digit hours 24 hours   means min Ute's:      mi 2 digits for minutes   second:      SS 2 digits in seconds 60 in   for quarter:    &NB Sp Q A number for quarterly (1-4)   There is also WW used to indicate the first weeks of the year in which W is used to denote the week of the month.     Current time minus 7 minutes   Select   Sysdate,sysdate -Interval ' 7 ' MINUTE  from  dual;  current time minus 7 hours   Select   Sysdate-interval ' 7 ' hour &nbs P;from dual;  Current time minus 7 days   select   sysdate-interval ' 7 ' Day  from dual;  current time minus July time &NB 　　 Sp Select   Sysdate,sysdate-interval ' 7 ' month  from dual;  current time minus 7 year time   select   Sysdate,sys Date-interval ' 7 ' year  from dual;  time interval multiplied by a number   select   sysdate,sysdate-8*interval ' 7 ' hour  from dual;             Select To_char (sysdate, ' Yyyy-mm-dd:hh24:mi:ss:pm:dy ') from dual;                       24 hours/day/afternoon week Chinese;      --Get November days--select to_char (to_date (' 2010-11-1 ', ' yyyy-mm-dd ')), ' DD ' from dual;  -Get December days--select to_char (to_date (' 2010-12-1 ', ' yyyy-mm-dd ')), ' DD ' from dual;       shows that last Monday to Sunday  select To_char (sysdate, ' YYYYMMDD')-to_number (To_char (sysdate, ' d ')-1)-6, To_char (sysdate, ' YYYYMMDD ')-to_number (To_char (sysdate, ' d ')-1)    from Dual



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