Replace CAD *Ranks table calculation with SQL window function

lib/auxiliary_data_computation.rb

@@ -50,58 +50,21 @@ def self.compute_rank_tables
       %w(average RanksAverage ConciseAverageResults),
     ].each do |field, table_name, concise_table_name|
       DbHelper.with_temp_table(table_name) do |temp_table_name|
-        current_country_by_wca_id = Person.current.pluck(:wca_id, :countryId).to_h
-        # Get all personal records (note: people that changed their country appear once for each country).
-        personal_records_with_event = ActiveRecord::Base.connection.execute <<-SQL
-          SELECT eventId, personId, countryId, continentId, min(#{field}) value
-          FROM #{concise_table_name}
-          GROUP BY personId, countryId, continentId, eventId
-          ORDER BY eventId, value
+        ActiveRecord::Base.connection.execute <<-SQL
+          INSERT INTO #{temp_table_name} (personId, eventId, best, worldRank, continentRank, countryRank)
+          WITH personal_best AS (
+            SELECT eventId, personId, countryId, continentId, min(#{field}) `value`
+            FROM #{concise_table_name}
+            GROUP BY personId, countryId, continentId, eventId
+          )
+          SELECT
+            personId, eventId, `value`,
+            RANK() OVER(PARTITION BY eventId ORDER BY `value`) AS worldRank,
+            RANK() OVER(PARTITION BY eventId, continentId ORDER BY `value`) AS continentRank,
+            RANK() OVER(PARTITION BY eventId, countryId ORDER BY `value`) AS countryRank
+          FROM personal_best
+          ORDER BY eventId, `value`
         SQL
-        personal_records_with_event.group_by(&:first).each do |event_id, personal_records|
-          personal_rank = Hash.new { |h, k| h[k] = {} }
-          ranked = Hash.new { |h, k| h[k] = {} }
-          counter = Hash.new(0)
-          current_rank = Hash.new(0)
-          previous_value = {}
-          personal_records.each do |_, person_id, country_id, continent_id, value|
-            # Update the region states (unless we have ranked this person already,
-            # e.g. 2008SEAR01 twice in North America and World because of his two countries).
-            ["World", continent_id, country_id].each do |region|
-              next if ranked[region][person_id]
-              counter[region] += 1
-              # As we ordered by value it can either be greater or tie the previous one.
-              current_rank[region] = counter[region] if previous_value[region].nil? || value > previous_value[region]
-              previous_value[region] = value
-              ranked[region][person_id] = true
-            end
-            cached_country = Country.c_find(current_country_by_wca_id[person_id])
-            # The only known case where this happens if current_country_by_wca_id[person_id] is nil,
-            # in other words, the personId from the Concise*Results table is not found in the Persons table.
-            # In the past, this has occurred when temporary results have been inserted for newcomers.
-            next if cached_country.nil?
-            # Set the person's data (first time the current location is matched).
-            personal_rank[person_id][:best] ||= value
-            personal_rank[person_id][:world_rank] ||= current_rank["World"]
-            if continent_id == cached_country.continentId
-              personal_rank[person_id][:continent_rank] ||= current_rank[continent_id]
-            end
-            if country_id == cached_country.id
-              personal_rank[person_id][:country_rank] ||= current_rank[country_id]
-            end
-          end
-          values = personal_rank.map do |person_id, rank_data|
-            # NOTE: continent_rank and country_rank may be not present because of a country change, in such case we default to 0.
-            "('#{person_id}', '#{event_id}', #{rank_data[:best]}, #{rank_data[:world_rank]}, #{rank_data[:continent_rank] || 0}, #{rank_data[:country_rank] || 0})"
-          end
-          # Insert 500 rows at once to avoid running into too long query.
-          values.each_slice(500) do |values_subset|
-            ActiveRecord::Base.connection.execute <<-SQL
-              INSERT INTO #{temp_table_name} (personId, eventId, best, worldRank, continentRank, countryRank) VALUES
-              #{values_subset.join(",\n")}
-            SQL
-          end
-        end
       end
     end
   end