从 firebird 2.5 中的周数获取开始和结束日期

Question

我在一列中有周数，我想生成另外两个列来显示周开始日期和周结束日期。

我的table:

| week_nr |  year_nr  |
+---------+-----------+
|    2    |   2018    |
|    5    |   2018    |

我想生成这个table

| week_nr  |  year_nr  | week_start  |  week_end   |
+----------+-----------+-------------+-------------+
|    2     |    2018   |  08.01.2018 |  14.01.2018 |
|    5     |    2018   |  29.01.2018 |  04.02.2018 |

我尝试使用 "extract" 命令获取日期，但无法正常工作。有谁知道 Firebird 2.5 的解决方案吗？

Answer 1

Firebird 中没有任何内置功能可以根据周数计算日期，您必须自己编写或找到一个现有的 UDF 来为您完成（例如 FreeAdhocUDF 中的 F_FIRSTDAYKW）。

例如，使用 Firebird 3(!) 存储函数，您可以：

create function mondayOfIsoWeek(isoYear integer, isoWeek integer)
  returns date
as
declare firstJanuary date;
declare firstThursday date;
declare firstWeek integer;
declare targetThursday date;
declare targetMonday date;
begin
  firstJanuary = cast(isoYear || '-01-01' as date);
  -- Thursday in the same week as the first of January
  -- This is either in week 1 or the last week of the previous year
  -- NOTE: 4 is Thursday
  firstThursday = dateadd(day, 4 - extract(weekday from firstJanuary), firstJanuary);
  firstWeek = extract(week from firstThursday);
  -- Already in first week of year, compensate
  if (firstWeek = 1) then
    isoWeek = isoWeek - 1;
  targetThursday = dateadd(week, isoWeek, firstThursday);
  targetMonday = dateadd(day, -3, targetThursday);
  return targetMonday;
end

Firebird 3 存储函数不能在 Firebird 2.5 中使用，但您可以将其用作存储过程的起点或执行您需要的执行块。如果绝对必要，您甚至可以将所有这些计算内联到一个表达式中（但这将非常不可读）。

从 firebird 2.5 中的周数获取开始和结束日期

Get begin & end date from week number in firebird 2.5

sql

firebird

firebird2.5