1.該函數返回當前的日期與時間,一般和dual偽表一起合作,

2.sysdate函數用于獲取數據庫所在的操作系統的當前時間值的.

我們可以使用NLS_DATE_FORMAT參數或者TO_CHAR函數來獲得我們想要的SYSDATE日期格式，具體的格式代碼如下：

Format Code Explanation

YEAR	Year, spelled out
YYYY	4-digit year
MM	Month (01-12; JAN = 01).
MON	Abbreviated name of month.
MONTH	Name of month, padded with blanks to length of 9 characters.
D	Day of week (1-7).
DAY	Name of day.
DD	Day of month (1-31).
DDD	Day of year (1-366).
DY	Abbreviated name of day.
HH	Hour of day (1-12).
HH12	Hour of day (1-12).
HH24	Hour of day (0-23).
MI	Minute (0-59).
SS	Second (0-59).
SSSSS	Seconds past midnight (0-86399).

3.與sysdate不同,CURRENT_DATE()函數會返回數據庫會話所設置的本地時區的當前日期.

4.設置nls_date_format的時間格式

alter session set nls_date_format='YYYY-MM-DD HH24:MI:SS';

另外請注意SYSDATE函數的類型并非是DATE類型，而是其特有的類型:

    SQL> create table mytime(t1 date);

Table created.

SQL> insert into mytime values (sysdate);

1 row created.

SQL> commit;

Commit complete.

SQL> select dump(t1), dump(sysdate), dump( current_date) from mytime;

DUMP(T1)
--------------------------------------------------------------------------------
DUMP(SYSDATE)
--------------------------------------------------------------------------------
DUMP(CURRENT_DATE)
--------------------------------------------------------------------------------
Typ=12 Len=7: 120,111,8,24,21,31,59
Typ=13 Len=8: 219,7,8,24,20,32,12,0
Typ=13 Len=8: 219,7,8,24,20,32,12,0

以上可以看到sysdate和current_date都屬于TYPE=13，而普通DATE類型為TYPE=12
  

數據類型type=12代表DATE Valid date range from January 1, 4712 BC to December 31, 9999 AD.

11.26號----sysdate函數