Identify and mark record times using SQL - mysql

Question

Given a database table that contains a list of race times, I need to be able to identify which of the performances are faster than earlier finish times for that athlete at a specific distance, e.g. it was their best time at the time of the performance.
Also, would it be better to update this and store as a boolean in an additional column at rest, rather than trying to calculate when doing a SELECT. The database isn't populated in chronological order, so not sure if a TRIGGER would help. I was thinking of a query that runs on the whole table after any inserts/updates. Appreciate this may have a performance impact, so could be run periodically rather than on each row update.
This is on a MySQL 5.6.47 server.
Example table
athleteId date distance finishTime
1 2020-01-04 5K 30:00
1 2020-01-11 5K 30:09
1 2020-01-18 5K 29:45
1 2020-01-25 5K 29:32
1 2020-02-01 5K 31:18
1 2020-02-02 10K 1:06:07
1 2020-02-08 5K 28:25
1 2020-02-23 10K 1:06:02
1 2020-02-23 10K 1:07:30
Expected output
athleteId date distance finishTime isPersonalBest
1 2020-01-04 5K 30:00 Y
1 2020-01-11 5K 30:09 N
1 2020-01-18 5K 29:45 Y
1 2020-01-25 5K 29:32 Y
1 2020-02-01 5K 31:18 N
1 2020-02-02 10K 1:06:07 Y
1 2020-02-08 5K 28:25 Y
1 2020-02-23 10K 1:06:02 Y
1 2020-02-23 10K 1:07:30 N
The data is just an example. The actual finish times are stored in seconds. There will be many more athletes and different event distances. If a performance is the first for that athlete at that distance, it would be classed as a personal best.

Answer 1

If you are running MysQL 8.0, you can use window functions:
select
t.*,
case when finishTime < min(finishTime) over(
partition by athleteId, distance
order by date
rows between unbounded preceding and 1 preceding
)
then 'Y'
else 'N'
end isPersonalBest
from mytable t
In earlier versions, one option is a correlated subquery:
select
t.*,
case when exists(
select 1
from mytable t1
where
t1.athleteId = t.athleteId
and t1.distance = t.distance
and t1.date < t.date
and t1.finishTime <= t.finishTime
)
then 'N'
else 'Y'
end isPersonalBest
from mytable t
I wouldn't recommend actually storing this derived information. Instead, you use the above query to create a view.

Answer 2

You can use a cumulative min in MySQL 8+:
select t.*,
(case when finishTime >=
min(finishTime) over (partition by athleteid, distance
order by date
rows between unbounded preceding and 1 preceding
)
then 'N' else 'Y'
end) as isPersonalBest
from t;
Here is a db<>fiddle.
In earlier versions, you could use not exists:
select t.*,
(case when not exists (select 1
from t t2
where t2.atheleteid = t.athleteid and
t2.distance = t.distance and
t2.date < t.date and
t2.finishTime <= t.finishTime
)
then 'Y' else 'N'
end) as isPersonalBest
from t;