Oracle To_Date Function 由文字格式轉成日期格式

 to_date function ：由文字格式轉換成日期格式
在使用此函式時，可以下列 SQL 來查詢目前的日期格式為何：

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SELECT parameter, value FROM v$nls_parameters where parameter='NLS_TIMESTAMP_TZ_FORMAT';   select to_char(sysdate,'DD-MON-RR') from dual;   select to_date('06-9月-10') from dual;

to_date function 語法如下：
to_date( string1, [ format_mask ], [ nls_language ] )

• string1 ：文字格式的日期
• format_mask ：選用，將  string1 轉換成此格式的日期
• nls_language is optional： This is the nls language used to convert string1 to a date.

 The following is a list of options for the format_mask parameter. These parameters can be used in many combinations.

Parameter	Explanation
YEAR	Year, spelled out
YYYY	4-digit year
YYY YY Y	Last 3, 2, or 1 digit(s) of year.
IYY IY I	Last 3, 2, or 1 digit(s) of ISO year.
IYYY	4-digit year based on the ISO standard
RRRR	Accepts a 2-digit year and returns a 4-digit year. A value between 0-49 will return a 20xx year. A value between 50-99 will return a 19xx year.
Q	Quarter of year (1, 2, 3, 4; JAN-MAR = 1).
MM	Month (01-12; JAN = 01).
MON	Abbreviated name of month. 簡短月份
MONTH	Name of month, padded with blanks to length of 9 characters.
RM	Roman numeral month (I-XII; JAN = I).
WW	Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.
W	Week of month (1-5) where week 1 starts on the first day of the month and ends on the seventh.
IW	Week of year (1-52 or 1-53) based on the ISO standard.
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.
J	Julian day; the number of days since January 1, 4712 BC.
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).
FF	Fractional seconds. Use a value from 1 to 9 after FF to indicate the number of digits in the fractional seconds. For example, 'FF4'.
AM, A.M., PM, or P.M.	Meridian indicator
AD or A.D	AD indicator
BC or B.C.	BC indicator
TZD	Daylight savings information. For example, 'PST'
TZH	Time zone hour.
TZM	Time zone minute.
TZR	Time zone region.

參考文章：http://www.techonthenet.com/oracle/functions/to_date.php