How to get sum of all running jobs from start time to end time?

Question

I have this table with millions of records:

I want to get the sum of all running jobs from Start Time to End Time. For example query 1: Between 1:00 and 4:00 how many jobs were running? Then here the answer will be 3 (Job1, Job2 & Job7).

I can use joins but want the approach that takes least time for millions of records.

Answer 1

You can write a subquery that gets your job COUNT between your start and end times along with a GROUP_CONCAT to group all of your jobs in a single, comma delimited row:

SELECT jobs AS "Jobs", job_count AS "Job Count"
FROM
(
SELECT
  1,
  GROUP_CONCAT(job SEPARATOR ', ') as jobs,
  COUNT(job) AS job_count
FROM
  sample_table 
WHERE
  start_time >= '1:00'
  AND
  end_time <= '4:00'
GROUP BY
  1
) a

Result:

Jobs	Job Count
Job1, Job2, Job7	3

Alternatively, you can use a CTE:

WITH cte AS (SELECT
  1,
  GROUP_CONCAT(job SEPARATOR ', ') as jobs,
  COUNT(job) AS job_count
FROM
  sample_table 
WHERE
  start_time >= '1:00'
  AND
  end_time <= '4:00'
GROUP BY
  1
) SELECT jobs AS "Jobs", job_count AS "Job Count" FROM cte

Result:

Jobs	Job Count
Job1, Job2, Job7	3

db<>fiddle here.

Notes:

• I used a dummy value of 1 for the grouping which is why I used a subquery and CTE, if you don't mind outputting the column you can remove the subquery or CTE.

• You can add a DISTINCT and ORDER BY attributes to the GROUP_CONCAT but this will likely impact your performance.

GROUP_CONCAT(DISTINCT job ORDER BY job ASC SEPARATOR ', ')

• Since you're dealing with a large dataset, I would ensure your table is properly indexed. I'm not sure what your key columns are but setting up indexes will speed up the query. See How MySQL Uses Indexes.