来自 ISO Week (201905) BigQuery 的提取日期

Question

I need to extract date of Sunday from it's ISO Week number: ie 201905 It needs to be in #standardSQL as it's going to be scheduled with scripts that don't support legacy.

I tried adjust working formula from Google Sheets but can't figure it out. The original formula from Google Sheets:

TO_TEXT (
(DATE(LEFT(Week_ISO,4),1,1)
- (WEEKDAY(DATE(LEFT(Week_ISO,4),1,1))-2)
+ (RIGHT(Week_ISO,2)-1)*7) 
+6)

Answer 1

From my reading of the documentation, this should work:

PARSE_DATE('%G%V', isoyyyymm)

But it doesn't.

So, here is an alternative:

SELECT DATE_ADD(DATE_TRUNC(PARSE_DATE('%Y%m%d', CONCAT(substr(isoyyyyww, 1, 4), '0601')),
                           isoyear
                          ),
                INTERVAL CAST(substr(isoyyyyww, -2) as int64) WEEK
               )
FROM (SELECT '200506' as isoyyyyww);

The idea here is the following:

• Convert your yyyyww format into a date in the middle of the year.
• Truncate the date to the beginning of the ISO year.
• Add back the appropriate number of weeks.

You can adapt this if your value is a number rather than a string.

Answer 2

The other option for me was to just not change to ISOWEEK. The iso week loses the year information anyway. Instead I just floored all dates to the first day of the ISOWEEK.

DATE_ADD(
  LAST_DAY(DATETIME(date), ISOWEEK), 
  INTERVAL 
  -6 
  DAY) as login_week

Answer 3

It seems your proposition is not totally right. For instance, it's not working for the week 200101. With your formula, the answer is 2001-01-08.

Here is my suggestion :

SELECT  DATE_ADD(DATE_TRUNC(PARSE_DATE('%Y%m%d', CONCAT(substr(isoyyyyww, 1, 4), '0104')),isoyear), INTERVAL CAST(substr(isoyyyyww, -2) as int64)-1 WEEK)
FROM (SELECT '200506' as isoyyyyww);