Calculating difference between min value and each row's value - mysql

Question

I have a database table which has a person's id, name, and time (in milliseconds, stored as an int). For example:
| id | name | totalTime |
| --- | ------ | --------- |
| 1 | Bob | 16280 |
| 2 | Andy | 17210 |
| 3 | Bill | 15320 |
| 4 | Matt | 14440 |
| 5 | Steven | 17570 |
| 6 | Tom | NULL |
| 7 | Angus | 17210 |
| 8 | Will | NULL |
| 9 | Jack | 17410 |
| 10 | Alex | 16830 |
Not necessarily all people have a time (thus the nulls).
I would like to have another two columns - one which shows the rank/position of each person, and another which shows the difference in time (milliseconds) between the best (i.e. minimum) time and each row's time.
I have managed to write a MySQL 8.x query which does the ranks:
SELECT id, name, totalTime,
(CASE WHEN totalTime IS NOT NULL THEN RANK() OVER ( PARTITION BY (CASE WHEN totalTime IS NOT NULL THEN 1 ELSE 0 END) ORDER BY totalTime ) END) totalRank
FROM results
ORDER BY -totalRank DESC;
...and outputs this:
| id | name | totalTime | totalRank |
| --- | ------ | --------- | --------- |
| 4 | Matt | 14440 | 1 |
| 3 | Bill | 15320 | 2 |
| 1 | Bob | 16280 | 3 |
| 10 | Alex | 16830 | 4 |
| 2 | Andy | 17210 | 5 |
| 7 | Angus | 17210 | 5 |
| 9 | Jack | 17410 | 7 |
| 5 | Steven | 17570 | 8 |
| 6 | Tom | NULL | NULL |
| 8 | Will | NULL | NULL |
...but have not been able to figure out the SQL to add another column with the time difference.
Below is an example of what I would like, but can't figure out how to do:
| id | name | totalTime | totalRank | difference |
| --- | ------ | --------- | --------- | ---------- |
| 4 | Matt | 14440 | 1 | 0 |
| 3 | Bill | 15320 | 2 | 880 |
| 1 | Bob | 16280 | 3 | 1840 |
| 10 | Alex | 16830 | 4 | 2390 |
| 2 | Andy | 17210 | 5 | 2770 |
| 7 | Angus | 17210 | 5 | 2770 |
| 9 | Jack | 17410 | 7 | 2970 |
| 5 | Steven | 17570 | 8 | 3130 |
| 6 | Tom | NULL | NULL | NULL |
| 8 | Will | NULL | NULL | NULL |
I have this available as a DB Fiddle: https://www.db-fiddle.com/f/gQvSeij2EKSufYp9VjbDav/0
Thanks in advance for any help!

Answer 1

You can use a CTE to get the min totalTime and use it to calculate the difference:
WITH cte as (SELECT MIN(totalTime) minTotalTime FROM results)
SELECT id, name, totalTime,
CASE WHEN totalTime IS NOT NULL
THEN RANK() OVER (PARTITION BY (
CASE
WHEN totalTime IS NOT NULL THEN 1
ELSE 0
END
) ORDER BY totalTime)
END totalRank,
totalTime - (SELECT minTotalTime from cte) difference
FROM results
ORDER BY -totalRank DESC;
See the demo.
Results:
| id | name | totalTime | totalRank | difference |
| --- | ------ | --------- | --------- | ---------- |
| 4 | Matt | 14440 | 1 | 0 |
| 3 | Bill | 15320 | 2 | 880 |
| 1 | Bob | 16280 | 3 | 1840 |
| 10 | Alex | 16830 | 4 | 2390 |
| 2 | Andy | 17210 | 5 | 2770 |
| 7 | Angus | 17210 | 5 | 2770 |
| 9 | Jack | 17410 | 7 | 2970 |
| 5 | Steven | 17570 | 8 | 3130 |
| 6 | Tom | | | |
| 8 | Will | | | |

Answer 2

Add min() window function
SELECT id, name, totalTime,
(CASE WHEN totalTime IS NOT NULL THEN RANK() OVER ( PARTITION BY (CASE WHEN totalTime IS NOT NULL THEN 1 ELSE 0 END) ORDER BY totalTime ) END) totalRank
,totaltime - min(totaltime) over() diff
FROM results
ORDER BY -totalRank DESC;

Answer 3

SELECT subtable.id,
subtable.NAME,
subtable.totalTime,
subtable.diff,
IIF(subtable.totalTime IS NULL,NULL,subtable.rowno) as bisi
FROM (
select *,
ROW_NUMBER() OVER (ORDER BY totalTime desc) as rowno,
totalTime -
(
select min(rst.totalTime)
from results rst) as diff
from results) subtable;
I would do this way in MS-SQL or alternatively in MYSQL
SELECT subtable.id,
subtable.NAME,
subtable.totalTime,
subtable.diff,
IF (subtable.totalTime IS NULL, NULL, subtable.rowno) as bisi
FROM (
select *,
ROW_NUMBER() OVER (ORDER BY totalTime desc) as rowno,
totalTime -
(
select min(rst.totalTime)
from results rst) as diff
from results) subtable;

Answer 4

Serg's answer is correct. I would write it as:
SELECT id, name, totalTime,
(CASE WHEN totalTime IS NOT NULL
THEN RANK() OVER (PARTITION BY (totalTime IS NULL) ORDER BY totalTime)
END) as totalRank,
totaltime - MIN(totaltime) OVER() as diff
FROM results
ORDER BY (totalTime IS NOT NULL) DESC, totalRank;
The differences are:
Simplifying the PARTITION BY. You use CASE, but MySQL conveniently treats booleans as "real" values.
Expressing the ORDER BY in a more intuitive fashion.