Mysql：需要找到24小时内的所有间隙，但只显示繁忙时间之间的时间 -

Question

我使用下面的代码来查找 24 小时内的空闲时间。代码运行良好，但仅显示某些时间之间的间隙。 例如，如果我们的繁忙时间是 19:00 到 19:40，另一个繁忙时间是 20:30 到 21:00，我们需要显示以下结果：

free_time_start   free_time_end
00:00:00          19:40:00
19:40:00      20:30:00
21:00:00          24:00:00

但结果是：

19:40:00 20:30:00

表示结果仅显示繁忙时间之间的时间。从一天开始或一天结束时，不要在它们之前和之后显示。

我的代码：

SELECT
  
    last_time + INTERVAL 0 MINUTE AS free_time_start,
    time  - INTERVAL 0 MINUTE AS  free_time_end
FROM (
    SELECT
        sc.*,lag(time+ INTERVAL perclocko MINUTE ) OVER (PARTITION BY courses_id ORDER BY time) AS last_time
        
    FROM
        students_courses sc 

   
   
) s
WHERE last_time < time;

注意：每个时钟是每节课的持续时间。

我尝试向查询添加假行，如下所示：

Union 0,0,0,0,'00:00:00',30,1

但这行不通

Answer 1

演示示例：

CREATE TABLE timeslots (
  time_start TIME,
  time_end TIME,
  CHECK ('00:00:00' <= time_start),
  CHECK (time_start < time_end),
  CHECK (time_end <= '24:00:00')
);
INSERT INTO timeslots VALUES 
('19:00', '19:40'), ('20:30', '21:00');
SELECT * FROM timeslots;

时间_开始	时间结束
19:00:00	19:40:00
20:30:00	21:00:00

WITH
cte1 AS (
  SELECT '00:00:00' slot, 1 weight
  UNION ALL
  SELECT '24:00:00', -1
  UNION ALL
  SELECT time_start, -1 FROM timeslots
  UNION ALL
  SELECT time_end, 1 FROM timeslots
  ),
cte2 AS (
  SELECT slot, SUM(weight) OVER (ORDER BY slot) cum_sum
  FROM cte1
  ),
cte3 AS (
  SELECT slot, SUM(cum_sum) OVER (ORDER BY slot) cum_sum
  FROM cte2
  )
SELECT MIN(slot) free_time_start,
       MAX(slot) free_time_end 
FROM cte3 
GROUP BY cum_sum;

空闲时间开始	空闲时间结束
00:00:00	19:00:00
19:40:00	20:30:00
21:00:00	24:00:00

小提琴

查询假设没有重叠的时隙。