两个工作日之间的统计数据（周一至周五）答案

【问题标题】：Stats Between Two Weekdays (Mon - Fri)两个工作日之间的统计数据（周一至周五）
【发布时间】：2017-01-01 07:36:32
【问题描述】：

我有以下内容，存储在 Postgres 9.5.4 数据库中。

CREATE TABLE activity (
    id int primary key,
    cat_id smallint,
    start_date date,
    end_date date
);

INSERT INTO activity VALUES(5822, 1, '2016-07-01', '2016-07-01');
INSERT INTO activity VALUES(5824, 5, '2016-07-01', '2016-07-01');
INSERT INTO activity VALUES(5825, 4, '2016-07-01', '2016-07-01');
INSERT INTO activity VALUES(5840, 5, '2016-07-01', '2016-07-01');
INSERT INTO activity VALUES(5873, 5, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5875, 3, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5876, 5, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5882, 5, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5883, 5, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5888, 4, '2016-07-05', '2016-07-05');
INSERT INTO activity VALUES(5905, 4, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5908, 5, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5911, 5, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5912, 3, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5913, 4, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5915, 4, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5920, 4, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5923, 4, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5928, 5, '2016-07-06', '2016-07-06');
INSERT INTO activity VALUES(5949, 4, '2016-07-07', '2016-07-07');
INSERT INTO activity VALUES(5955, 5, '2016-07-07', '2016-07-07');
INSERT INTO activity VALUES(5959, 4, '2016-07-07', '2016-07-07');
INSERT INTO activity VALUES(5960, 2, '2016-07-07', '2016-07-07');
INSERT INTO activity VALUES(5965, 4, '2016-07-07', '2016-07-07');
INSERT INTO activity VALUES(5998, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6000, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6001, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6003, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6005, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6008, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6012, 4, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6016, 5, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6018, 5, '2016-07-11', '2016-07-11');
INSERT INTO activity VALUES(6032, 4, '2016-07-12', '2016-07-12');
INSERT INTO activity VALUES(6035, 5, '2016-07-12', '2016-07-12');
INSERT INTO activity VALUES(6052, 4, '2016-07-12', '2016-07-12');
INSERT INTO activity VALUES(6060, 4, '2016-07-12', '2016-07-12');
INSERT INTO activity VALUES(6070, 5, '2016-07-13', '2016-07-13');
INSERT INTO activity VALUES(6075, 5, '2016-07-13', '2016-07-11');
INSERT INTO activity VALUES(6076, 3, '2016-07-13', '2016-07-11');
INSERT INTO activity VALUES(6077, 5, '2016-07-13', '2016-07-11');
INSERT INTO activity VALUES(6078, 5, '2016-07-13', '2016-07-13');

我想收集一些关于两个工作日之间差异的统计数据（仅限周一至周五）。

这个查询可能对我想要实现的目标有所帮助。

SELECT 
    SUM(CASE WHEN cat_id = 5 THEN 1 ELSE 0 END)  as "# Cat 5",
    AVG(CASE WHEN cat_id = 5 THEN start_date - end_date END)  as "AVG Cat 5",
    MIN(CASE WHEN cat_id = 5 THEN start_date - end_date END)  as "MIN Cat 5",
    MAX(CASE WHEN cat_id = 5 THEN start_date - end_date END)  as "MAX Cat 5"
FROM activity

我还创建了一个SQL Fiddle，以帮助进行测试。

为了进一步描述这一点，假设一个活动在周六创建，并在周一完成，持续时间应该是 0 天（因为我们不包括周六和周日）。如果一个活动在周五创建并在周一完成，则持续时间为 1。

谢谢。

【问题讨论】：

您能否更详细地描述一下您所说的两个工作日之间差异的统计数据是什么意思？
我正在寻找每个类别所用天数的平均值、最小值和最大值。
工作日从何而来？
为了进一步描述这一点，假设一个活动在周六创建，并在周一完成，持续时间应该是 0 天（因为我们不包括周六和周日）。如果一项活动在周五创建并在周一完成，则持续时间为 1。我希望这会有所帮助吗？谢谢。
是的，现在更清楚了。也许您应该相应地更新问题。

标签： postgresql dayofweek postgresql-9.5

【解决方案1】：

您在此处尝试执行的操作可以使用 CTE 在纯 SQL 中完成。请参阅this answer 以计算距某个日期一定天数的工作日；你需要逆运算，但你会明白的。

不过，使用这个函数更容易、更快捷，从上面链接的答案中重新设计来计算两个日期之间的工作日数：

CREATE FUNCTION business_days_between(from_date date, to_date date) RETURNS int AS $$
-- This function assumes Mon-Fri business days. This returns an "open" range of days,
-- i.e. from Monday to Tuesday = 1. For a "closed" range of days (e.g. rentals), you
-- should add 1 to the result.
DECLARE
  alldays   int;   -- All calendar days in the period, counting down to 0
  days      int;   -- The working days to calculate, counting up from 0
  weeks     int;
  start_dow int;
  temp_date date;
BEGIN
  -- If from_date = to_date simply return 0.
  IF from_date = to_date THEN
    RETURN 0;
  END IF;

  -- If dates are reversed, flip them
  IF from_date > to_date THEN
    temp_date := from_date;
    from_date = to_date;
    to_date := temp_date;
  END IF;

  -- Set up variables, remove initial weekend days
  alldays := to_date - from_date;
  start_dow := extract(dow from from_date);
  IF start_dow = 0 THEN -- Don't count initial Sunday
    alldays := alldays - 1;
  END IF;
  IF start_dow = 6 THEN -- Fudge initial Saturday to the following Sunday
    start_dow := 0;
    alldays := alldays - 2;
  END IF;
  IF alldays <= 0 -- from_date is Saturday, to_date is next Sunday or Monday
    RETURN 0;
  END IF;

  -- Process the current week
  IF start_dow + alldays <= 5 THEN -- Stay in this week
    RETURN alldays;
  ELSE                             -- Count towards Friday
    days := 5 - start_dow;
    alldays := alldays - days;
  END IF;

  -- Move by full weeks
  weeks := alldays / 7;
  alldays := alldays - weeks * 7;
  days := days + weeks * 5;

  -- Add any remaining days, after the weekend
  IF alldays > 2 THEN
    days := days + alldays - 2;
  END IF;

  RETURN days;
END; $$ LANGUAGE plpgsql STRICT IMMUTABLE;

您的查询现在变为：

SELECT 
    count(*) as "# Cat 5",
    avg(business_days) AS "AVG Cat 5",
    min(business_days) AS "MIN Cat 5",
    max(business_days) AS "MAX Cat 5"
FROM (
  SELECT business_days_between(start_date, end_date) AS business_days
  FROM activity
  WHERE cat_id = 5) sub;

【讨论】：