行间时差

Question

In a mysql database (ver.5.7.15) I've got the following table named operation_list containing the following data: id ( autoincrement integer , primary key ), operation_date_time ( datetime ), operation ( enumerated values : START , STOP ), so the table looks like that:

+------+---------------------+-----------+
| id   | operation_date_time | operation |
+------+---------------------+-----------+
|    1 | 2000-01-01 06:30:45 | START     |
|    2 | 2000-01-01 07:45:00 | STOP      |
|    3 | 2000-01-01 08:18:12 | START     |
|    4 | 2000-01-01 11:23:58 | STOP      |
|    5 | 2000-01-01 15:45:01 | START     |
|    6 | 2000-01-01 19:01:33 | STOP      |
+------+---------------------+-----------+

Now, assuming that the first row is always a START, the last ROW is always a STOP, the STOP is always placed after a START, I need to retrieve the time difference between START and STOP in seconds. Hence, I need to write an SQL that would produce the following recordset:

+------+---------------------+-----------+
| id   | operation_date_time | duration  |
+------+---------------------+-----------+
|    1 | 2000-01-01 06:30:45 | 4455      |
|    3 | 2000-01-01 08:78:12 | 11146     |
|    5 | 2000-01-01 15:45:01 | 11792     |  
+------+---------------------+-----------+

Where 4455 is equivalent to 1 hour, 14 minutes and 15 seconds, 11146 is equivalent to 3 hours, 5 minutes and 46 seconds, 11792 is equivalent to 3 hours, 16 minutes and 32 seconds, and so on.

What's the best way to do it in a single SQL statement without creating additional tables or dedicated scripting?

Answer 1

This works IN mysql 5.X

But it is uglier as in 8.0

SELECT
   MIN(id) id
  ,MIN(`operation_date_time`) `operation_date_time`
  ,MAX(diff) duration  
FROM
(SELECT 
  id
  , IF(`operation` = 'START', 0,TIME_TO_SEC(TIMEDIFF(`operation_date_time`,  @datetime))) diff
  ,IF(`operation` = 'START',  @count := @count + 1,@count := @count) groupby
  ,@datetime := `operation_date_time` `operation_date_time`
 FROM
  (SELECT * FROM timetable ORDER by `operation_date_time` ASC) t1, (SELECT @datetime := NOW()) a,
   (SELECT @count := 0) b) t2
GROUP by groupby;

 CREATE TABLE timetable ( `id` INTEGER, `operation_date_time` VARCHAR(19), `operation` VARCHAR(5) ); INSERT INTO timetable (`id`, `operation_date_time`, `operation`) VALUES ('1', '2000-01-01 06:30:45', 'START'), ('2', '2000-01-01 07:45:00', 'STOP'), ('3', '2000-01-01 08:18:12', 'START'), ('4', '2000-01-01 11:23:58', 'STOP'), ('5', '2000-01-01 15:45:01', 'START'), ('6', '2000-01-01 19:01:33', 'STOP');

\n✓ \n\n✓ \n

SELECT MIN(id) id ,MIN(`operation_date_time`) `operation_date_time` ,MAX(diff) duration FROM (SELECT id , IF(`operation` = 'START', 0,TIME_TO_SEC(TIMEDIFF(`operation_date_time`, @datetime))) diff ,IF(`operation` = 'START', @count := @count + 1,@count := @count) groupby ,@datetime := `operation_date_time` `operation_date_time` FROM (SELECT * FROM timetable ORDER by `operation_date_time` ASC) t1, (SELECT @datetime := NOW()) a, (SELECT @count := 0) b) t2 GROUP by groupby;

\nid | operation_date_time |  duration\n-: |  :------------------ |  -------: \n 1 |  2000-01-01 06:30:45 |  4455 \n 3 |  2000-01-01 08:18:12 |  11146 \n 5 |  2000-01-01 15:45:01 |  11792 \n

db<>fiddle here

Answer 2

Use window functions to get the ending time. I am going to use a cumulative conditional min:

select t.*,
       timestampdiff(second, operation_date_time, stop_dt) as diff_seconds
from (select t.*,
             min(case when operation = 'STOP' then operation_date_time end) over (order by operation_date_time) as stop_dt
      from t
     ) t
where operation = 'START';

If the data really is interleaved, then you could just use lead() :

select t.*,
       timestampdiff(second, operation_date_time, stop_dt) as diff_seconds
from (select t.*,
             lead(operation_date_time) over (order by operation_date_time) as stop_dt
      from t
     ) t
where operation = 'START';

EDIT:

In MySQL pre-8.0:

select t.*,
       timestampdiff(second, operation_date_time, stop_dt) as diff_seconds
from (select t.*,
             (select min(t2.operation_date_time)
              from t t2
              where t2.operation = 'STOP' and
                    t2.operation_date_time > t.operation_date_time
             ) as stop_dt
      from t
     ) t
where operation = 'START';

Answer 3

SELECT operation_date_time,DURATION FROM ( SELECT *,DATEDIFF(SECOND,operation_date_time,LEAD(operation_date_time)OVER(ORDER BY ID)) AS DURATION FROM PRACTICE )A WHERE operation='START'