Add index to student_races table

db/migrate/20220822214951_add_index_to_student_races.rb

@@ -0,0 +1,5 @@
+class AddIndexToStudentRaces < ActiveRecord::Migration[7.0]
+  def change
+    add_index :student_races, %i[student_id race_id]
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2022_08_09_213959) do
+ActiveRecord::Schema[7.0].define(version: 2022_08_22_214951) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
   enable_extension "plpgsql"
@@ -371,6 +371,7 @@ ActiveRecord::Schema[7.0].define(version: 2022_08_09_213959) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["race_id"], name: "index_student_races_on_race_id"
+    t.index ["student_id", "race_id"], name: "index_student_races_on_student_id_and_race_id"
     t.index ["student_id"], name: "index_student_races_on_student_id"
   end