On 29-8-2020 19:04, Lyle H. Gray wrote:
Jim H <invalid@invalid.invalid> wrote in news:mlvkkfhv1d4kvorvga6jhoj959pp44j3uu@4ax.com:
IIRC iso weeks start on Monday, ordinary weeks start on Sunday.
Look at the linux 'date' command, specifically %V (%G) and %U
That may suggest why 20210101 is isoweek 53.
As I (think I) recall... you can get the ISO week by counting
Thursdays in the year to date.
The first "full" week of the year under ISO standard 8601 is the first week with four days/first week with a Thursday in it (ISO weeks start on Monday, not Sunday, as noted above).
In this group, though, we should be talking about the functions WEEK(), YEARWEEK(), and WEEKOFYEAR(), not DATEPART(), since MySQL doesn't have a DATEPART() function.
WITH RECURSIVE days as (
SELECT cast('2021-01-01' as date) d
union all
SELECT date_add(d,INTERVAL 1 day) from days where d < '2021-01-06')
select
d, week(d),
week(d,0) W0,
week(d,1) W1,
week(d,2) W2,
week(d,3) W3,
week(d,4) W4,
week(d,5) W5,
week(d,6) W6,
week(d,7) W7,
weekofyear(d) WOY,
yearweek(d) YOW,
yearweek(d,0) YOW0,
yearweek(d,1) YOW1
FROM days;
(output, in CSV):
d , week(d) , W0 , W1 , W2 , W3 , W4 , W5 , W6 , W7 , WOY , YOW , YOW0 , YOW1 2021-01-01 , 0 , 0 , 0 , 52 , 53 , 0 , 0 , 53 , 52 , 53 , 202052 , 202052 , 202053
2021-01-02 , 0 , 0 , 0 , 52 , 53 , 0 , 0 , 53 , 52 , 53 , 202052 , 202052 , 202053
2021-01-03 , 1 , 1 , 0 , 1 , 53 , 1 , 0 , 1 , 52 , 53 , 202101 , 202101 , 202053
2021-01-04 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 202101 , 202101 , 202101 2021-01-05 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 202101 , 202101 , 202101 2021-01-06 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 1 , 202101 , 202101 , 202101
conclusion, there is nothing to laugh about ...
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