Hi all again,
I would like to propose the removal of the WEEK() and WEEKOFYEAR()
functions from Drizzle and the corresponding default_week_format session
variable, sometimes called the "week mode".
Details of these things in MySQL can be found here:
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_week
http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_weekofyear
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_default_week_format
Why am I proposing this? A number of reasons:
1) Simplify the date functions
2) Standardize to format specifiers available in the C std library for
strftime()
3) Removal of custom code that duplicates the strftime() and mktime()
functions in cstdlib (about 1000 lines of code).
Will there be any loss of functionality?
No. At least not any functionality that makes sense. :)
The DATE_FORMAT() function has specifiers which enable getting the week
number in three formats which correspond to the strftime() format
specifiers:
%U returns the week number 00-53 where week 1 is the first week
containing a Sunday. Days in a week preceding the first Sunday are in
week 0.
%W returns the week number 00-53 where week 1 is the first week
containing a Monday. Days in a week preceding the first Monday are in
week 0.
%V returns the week number of the year (Monday as the first day of the
week) as a decimal number [01,53]. If the week containing 1 January has
four or more days in the new year, then it is considered week 1.
Otherwise, it is the last week of the previous year, and the next week
is week 1. This format is the format specified by ISO8601:1988.
Currently, the WEEK() function is, IMHO, overly complex and mostly
redundant with DATE_FORMAT() given one of the specifiers above. It uses
a week_mode second argument, which influences the return of the function
per the following table:
Mode First day of week Range Week 1 is the first week...
------ ------------------- ------- -------------------------------
0 Sunday 0-53 with a Sunday in this year
1 Monday 0-53 with more than 3 days this year
2 Sunday 1-53 with a Sunday in this year
3 Monday 1-53 with more than 3 days this year
4 Sunday 0-53 with more than 3 days this year
5 Monday 0-53 with a Monday in this year
6 Sunday 1-53 with more than 3 days this year
7 Monday 1-53 with a Monday in this year
If we removed the WEEK() function and week_mode variable entirely, the
only supported behaviours would be modes 0, 3, and 5. All other modes
correspond to behaviour that is contrary to any standard.
ISO8601:1988 dictates that the first week is the one containing more
than 3 days in a year, and that Monday is the start of the week and week
numbers are numbered 1-53. Therefore modes 1, 4, and 6 produce
behaviour that is actually dangerous: it pretends to be ISO8601, but
isn't correct.
Therefore, I propose the removal of WEEK() and week_mode.
Here is how one might produce the identical result to WEEK() for modes
0, 3, and 5 using DATE_FORMAT() properly:
# "mode 0"
SELECT DATE_FORMAT("2008-01-01", "%U")+0;
# "mode 3"
SELECT DATE_FORMAT("2008-01-01", "%V")+0;
# "mode 5"
SELECT DATE_FORMAT("2008-01-01", "%W")+0;
Please vote for whether my proposal has merit.
Thanks,
Jay
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