# Get all personal records, grouping for each person by event, event+continent, and event+continent+country
WITH personal_bests AS (
   SELECT personId, 
      eventId,
      continentId,
      countryId, 
      MIN(best) AS value
   FROM ConciseSingleResults
   GROUP BY personId,
      eventId,
      continentId,
      countryId
   WITH ROLLUP
   HAVING eventId IS NOT NULL
),
# Calculate all rankings via RANK(). worldRank ranks over the best results for each person by event. continentRank ranks over the best result for each person by event+continent. countryRank ranks over the best result for each person by event+continent+country. If someone changes country and/or continent, their results from the previous region still count towards the rankings for others in that region, however do not count towards their own regional ranking. Regional rankings are marked as NULL if they do not match the person's present region of representation.

ranking_calculations AS (
   SELECT personId,
      eventId,
      value,
      CASE WHEN pb.continentId IS NULL
         THEN RANK() OVER(PARTITION BY eventId
            ORDER BY CASE WHEN pb.continentId IS NULL THEN 0 ELSE 1 END, value)
         END AS worldRank,
      CASE WHEN pb.countryId IS NULL AND co.continentId = pb.continentId
         THEN RANK() OVER(PARTITION BY eventId, pb.continentId
            ORDER BY CASE WHEN pb.countryId IS NULL AND pb.continentId IS NOT NULL THEN 0 ELSE 1 END, value) 
         END AS continentRank,
      CASE WHEN pb.countryId IS NOT NULL AND p.countryId = pb.countryId
          THEN RANK() OVER(PARTITION BY eventId, pb.countryId
             ORDER BY CASE WHEN pb.countryId IS NOT NULL THEN 0 ELSE 1 END, value)
          END AS countryRank
   FROM personal_bests pb
   JOIN Persons p
      ON p.wca_id = pb.personId
         AND p.subId = 1
   JOIN Countries co
     ON co.id = p.countryId
)

# Group again by person to combine the world/continent/country rankings for each person. If someone has changed region of representation, their ranking is per the fastest result achieved under their present region. If they have not achieved any results in an event since changing their region, their rank is stored as 0.
SELECT personId,
   eventId,
   MIN(value) AS best,
   MIN(worldRank) AS worldRank,
   IFNULL(MIN(continentRank), 0) AS continentRank,
   IFNULL(MIN(countryRank), 0) AS countryRank
FROM ranking_calculations
GROUP BY personId,
   eventId
ORDER BY eventId,
   worldRank