Oracle to_char的一些功能记录。
1、转成年月日时分秒的操作；
2、转成微妙的操作
SQL> select to_char(systimestamp, 'yyyy-mm-dd-hh24:mi:ss.ff') from dual;
TO_CHAR(SYSTIMESTAMP,'YYYY-MM-
------------------------------
2013-09-26-16:08:04.234000
注意，没有转成毫秒的参数格式。
如果需要转成毫秒，这样操作
SQL> select to_char(systimestamp, 'yyyy-mm-dd-hh24:mi:ss.ff3') from dual;
TO_CHAR(SYSTIMESTAMP,'YYYY-MM-
------------------------------
2013-09-26-16:12:10.640
3、转成零点到当前时间的秒数
SQL> select to_char(systimestamp, 'yyyymmddhh24miss -- SSSSS') from dual;
TO_CHAR(SYSTIMESTAMP,'YYYYMMDD
------------------------------
20130926160938 -- 58178
SQL> select to_char(systimestamp, 'yyyy-mm-dd-hh24:mi:ss'),
2 to_char(systimestamp, 'yyyymmddhh24miss -- SSSSS'),
3 to_char(systimestamp, 'hh24') * 60 * 60 +
4 to_char(systimestamp, 'mi') * 60 + to_char(systimestamp, 'ss') +
5 to_number(to_char(systimestamp, 'ff') / 1000000.00)
6 from dual
7 /
TO_CHAR(SYSTIMESTAMP,'YYYY-MM- TO_CHAR(SYSTIMESTAMP,'YYYYMMDD TO_CHAR(SYSTIMESTAMP,'HH24')*6
------------------------------ ------------------------------ ------------------------------
2013-09-26-16:00:13 20130926160013 -- 57613 57613
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其他参数如下表所示：
ParameterExplanation 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 Q Quarter of year (1, 2, 3, 4; JAN-MAR = 1). MM Month (01-12; JAN = 01). MON Abbreviated name of month. 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.
其他语言objective-c的date格式转换，参考
http://userguide.icu-project.org/formatparse/datetime