Postgresql 两个工作日（周一至周五）之间的统计数据

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（仅周一至周五）之间差异的统计数据

这个查询可能有助于实现我的目标

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，以帮助测试

---

为了进一步描述这一点，假设一项活动在周六创建，并在周一完成，持续时间应为0天（因为我们不包括周六和周日）。如果一项活动是在星期五创建并在星期一完成的，则持续时间为1

---

谢谢。

您在这里尝试的操作可以使用CTE在纯SQL中完成。请参阅，以计算距某个日期一定天数的工作日；你需要逆运算，但你会得到要点

不过，使用此函数更容易、更快捷，它是根据上述链接答案重新编写的，用于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;

---

你能更详细地描述一下你所说的两个工作日之间差异的统计数字是什么意思吗？我在寻找每个类别的平均天数、最小天数和最大天数。工作日从何而来？为了进一步描述这一点，假设一项活动在周六创建，并在周一完成，持续时间应为0天（因为我们不包括周六和周日）。如果一项活动是在星期五创建并在星期一完成的，则持续时间为1。我希望这有帮助？谢谢。是的，现在更清楚了。也许你应该相应地更新这个问题。

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;