diff --git a/lib/tasks/statistic_subject_info.rake b/lib/tasks/statistic_subject_info.rake
index f8784d8fe..363570d18 100644
--- a/lib/tasks/statistic_subject_info.rake
+++ b/lib/tasks/statistic_subject_info.rake
@@ -9,9 +9,9 @@ namespace :subjects do
         "school_used_count, created_at, updated_at"
     subjects.find_in_batches(batch_size: 50) do |s|
       Parallel.each_with_index(s, in_processes: 4) do |subject, index|
-        if subject == s.first
-          buffer_size == 0
-          str == ""
+        if defined?(buffer_size).nil?
+          buffer_size = 0
+          str = ""
         end
         buffer_size += 1
         str += ", " unless str.empty?