Select Status That Last for More Than 1 Second - mysql

Question

I have got a problem looks simple, but I could not find the solution.
So, I have got a table with two cols like this:
Time Status
00:00:00.111 Off
00:00:00.222 On
00:00:00.345 On
00:00:01.555 On
00:00:01.666 Off
00:00:02.222 On
00:00:02.422 On
00:00:02.622 Off
00:00:05.888 Off
00:00:05.999 Off
I want to select all statuses of On which lasted for more than 1 second,
in this example, I want the sequence:
00:00:00.222 On
00:00:00.345 On
00:00:01.555 On
Could you guys give me any clue? Many thanks!

Answer 1

A simple GROUP BY and SUM can not do this on your current dataset, so my idea is to add a helper column:
CREATE TABLE someTable(
`time` DATETIME,
status CHAR(3),
helperCol INT
);
The helperCol is an INT and will be set as follows:
CREATE PROCEDURE setHelperCol()
BEGIN
DECLARE finished,v_helperCol INT;
DECLARE status CHAR(3);
DECLARE ts DATETIME;
DECLARE CURSOR st FOR SELECT `time`,status,helperCol FROM someTable WHERE helperCol IS NOT NULL; -- Handy for re-use: No need to go over all data, so you can save the helperCol as permanent value.
DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;
SELECT #maxVal:=MAX(helperCol) FROM helperCol;
SET finished=0;
SET helperCol=#maxVal;
IF(!helperCol>0) SET helperCol=1;
OPEN st;
FETCH ts,status,v_helperCol FROM st;
WHILE(finished=0) DO
IF(status='Off') v_helperCol=v_helperCol+1;
UPDATE someTable SET helperCol=v_helperCol WHERE `time`=ts; -- Assuming `time` is unique;
FETCH ts,status,v_helperCol FROM st;
END WHILE;
CLOSE st;
END;
Execute the procedure and the result is:
Time Status helperCol
00:00:00.111 Off 2
00:00:00.222 On 2
00:00:00.345 On 2
00:00:01.555 On 2
00:00:01.666 Off 3
00:00:02.222 On 3
00:00:02.422 On 3
00:00:02.622 Off 4
This can now be grouped and processed:
SELECT MAX(`time`)-MIN(`time`) AS diffTime
FROM someTable
WHERE status='ON'
GROUP BY helperCol
HAVING MAX(`time`)-MIN(`time`)>1;
The result of that is (you need to search for the correct datetime functions to apply in the MAX-MIN part):
1.333
Alternative:
You can also process the MAX-MIN in the stored procedure, but that would not be efficiently repeatable as the helperColumn solution is.

Answer 2

SELECT a.time start
, MIN(c.time) end
, TIMEDIFF(MIN(c.time),a.time) duration
FROM
( SELECT x.*, COUNT(*) rank FROM my_table x JOIN my_table y ON y.time <= x.time GROUP BY time ) a
LEFT
JOIN
( SELECT x.*, COUNT(*) rank FROM my_table x JOIN my_table y ON y.time <= x.time GROUP BY time ) b
ON b.status = a.status
AND b.rank = a.rank - 1
JOIN
( SELECT x.*, COUNT(*) rank FROM my_table x JOIN my_table y ON y.time <= x.time GROUP BY time ) c
ON c.rank >= a.rank
LEFT
JOIN
( SELECT x.*, COUNT(*) rank FROM my_table x JOIN my_table y ON y.time <= x.time GROUP BY time ) d
ON d.status = c.status
AND d.rank = c.rank + 1
WHERE b.rank IS NULL
AND d.rank IS NULL
AND a.status = 1
GROUP
BY a.time
HAVING duration >= 1;
Another, faster, method might be along these lines - unfortunately I don't think the data types and functions in my version of MySQL support fractions of a second, so this is probably a little bit wrong (there may also be a logical error)...
SELECT time
, status
, cumulative
FROM
( SELECT *
, CASE WHEN #prev = status THEN #i:=#i+duration ELSE #i:=0 END cumulative
, #prev:=status
FROM
( SELECT x.*
, TIME_TO_SEC(MIN(y.time))-TIME_TO_SEC(x.time) duration
FROM my_table x
JOIN my_table y
ON y.time > x.time
GROUP
BY x.time
) n
ORDER
BY time
) a
WHERE cumulative >= 1
AND status = 1;