MySQL Daily Time Coverage Without Gaps - mysql

Question

I have a table like the following example:
What I need to do is return the coverage (number of hours an operator/s were onsite) for each day. The challenge is that I need to ignore gaps in coverage and not double count hours where two operators were signed in at the same time. For instance, the image below is a visual representation of the table.
The logic of the image is as follows:
Operator A: Signed in at 10 and signed out at noon for a total of 2 hours
Operator B: Signed in at 1 and signed out at 3 for a total of 2 hours
Operator A: Came back and signed in at 2 and signed out at 5 for a total of 3 hours but 1 hour overlaps with operator A so I cannot count that 1 hour otherwise I will be double counting coverage
Therefore the total coverage time without overlaps is 6 hours and the value I need the query to produce. So far I can ignore double counting by taking the max in min dates of each day and subtracting the two:
SELECT YEAR, WEEK, SUM(HOURS)
FROM
(SELECT
YEAR(SignedIn) AS YEAR,
WEEK(SignedIn) AS WEEK,
DAY(SignedIn) AS DAY,
time_to_sec(timediff(MAX(SignedOut), MIN(SignedIn)))/ 3600 AS HOURS
FROM OperatorLogs
GROUP BY YEAR, WEEK, DAY) As VirtualTable
GROUP BY YEAR, WEEK
Which produces 7 because it takes the first sign-in (10 AM) and calculates the hours up until the last sign-out (4:00 PM). However, it includes the gap in coverage (12 - 1) which should not be included. I am unsure of how to remove that time from the total hours while also not double counting when there is overlap, i.e. from 2-3 there should only be 1 hour of coverage even though two separate operators are on site each putting in an hour. Any help is appreciated.

Answer 1

Sorry, work interrupted me.
Here's my working solution, I'm not convinced it's optimal due to the (relatively) expensive nature of the joins, but I've optimised it slightly based on the soft-rule that "shifts" never span multiple days.
SELECT
calendar_date,
SUM(coverage_seconds) / 3600 AS coverage_hours
FROM
(
-- Signins that didn't happen within another operators shift
SELECT DISTINCT
DATE(e.signedin) AS calendar_date,
-(UNIX_TIMESTAMP(e.signedin) MOD 86400) AS coverage_seconds
FROM
OperatorLogs e
LEFT JOIN
OperatorLogs o
ON o.signedin >= DATE(e.signedin)
AND o.signedin < e.signedin
AND o.signedout >= e.signedin
WHERE
o.signedin IS NULL
UNION ALL
-- Signouts that didn't happen within another operators shift
SELECT DISTINCT
DATE(e.signedout) AS calendar_date,
+(UNIX_TIMESTAMP(e.signedout) MOD 86400) AS coverage_seconds
FROM
OperatorLogs e
LEFT JOIN
OperatorLogs o
ON o.signedin >= DATE(e.signedout)
AND o.signedin <= e.signedout
AND o.signedout > e.signedout
WHERE
o.signedin IS NULL
)
AS coverage_markers
GROUP BY
calendar_date
;
Feel free to test it with more rigourous data...
https://www.db-fiddle.com/f/4RgWVhcdNEro21rUksVdXD/0
(As a note, to make your sample data match your excel image, your first shift should have started at 9am)