【SQL基础】一年中的周次

select to_char(to_date('2009-07-10','YYYY-MM-DD'),'IW') from dual;

这个是ISO标准，从指定表中查询时不会出现重复的周次。

而用 select to_char(to_date('2009-07-10','YYYY-MM-DD'),'WW') from dual;

会出现重复周次。

待详究。

转载：

to_char(1210.73, '9999.9')	would return '1210.7'
to_char(1210.73, '9,999.99')	would return '1,210.73'
to_char(1210.73, '$9,999.00')	would return '$1,210.73'
to_char(21, '000099')	would return '000021'

 

The following is a list of valid parameters when the to_char function is used to convert a date to a string. These parameters can be used in many

   

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
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.