WEEKNUM
WEEKNUM 計算內部日期值當年的週數。
國際標準 ISO 8601 已頒佈星期一為每週的第一天。若有某週跨越某年和次年，則會根據該週大部分的天數落於哪一年來指定其為第幾週。亦即任何年度的第 1 週均會包含 1 月 4 日。
This function is part of the Open Document Format for Office Applications (OpenDocument) standard Version 1.2. (ISO/IEC 26300:2-2015)
ISOWEEKNUM(Number)
value 是日期的內部數值。
When entering dates as part of formulas, slashes or dashes used as date separators are interpreted as arithmetic operators. Therefore, dates entered in this format are not recognized as dates and result in erroneous calculations. To keep dates from being interpreted as parts of formulas use the DATE function, for example, DATE(1954;7;20), or place the date in quotation marks and use the ISO 8601 notation, for example, "1954-07-20". Avoid using locale dependent date formats such as "07/20/54", the calculation may produce errors if the document is loaded under different locale settings.
Unambiguous conversion is possible for ISO 8601 dates and times in their extended formats with separators. If a #VALUE! error occurs, then unselect Generate #VALUE! error in Collabora Office - PreferencesTools - Options - Collabora Office Calc - Formula, button Details... in section "Detailed Calculation Settings", Conversion from text to number list box.
=ISOWEEKNUM(DATE(1995;1;1)) returns 52. Week 1 starts on Monday, 1995-01-02.
=ISOWEEKNUM(DATE(1999;1;1)) returns 53. Week 1 starts on Monday, 1999-01-04.