diff --git a/lib/tasks/statistic_subject_info.rake b/lib/tasks/statistic_subject_info.rake
index 27496e719..d188011a7 100644
--- a/lib/tasks/statistic_subject_info.rake
+++ b/lib/tasks/statistic_subject_info.rake
@@ -5,12 +5,14 @@ namespace :subjects do
     puts("---------------------data_statistic_begin")
     Rails.logger.info("---------------------data_statistic_begin")
     subjects = Subject.where(status: 2, hidden: 0)
-    str = ""
-    buffer_size = 0
     column_value = "subject_id, study_count, course_study_count, initiative_study, passed_count, course_used_count, " +
         "school_used_count, created_at, updated_at"
     subjects.find_in_batches(batch_size: 50) do |s|
+      str = ""
+      buffer_size = 0
       Parallel.each(s, in_processes: 4) do |subject|
+        buffer_size += 1
+        str += ", " unless str.empty?
         puts("---------------------data_statistic: #{subject.id}")
         Rails.logger.info("---------------------data_statistic: #{subject.id}")
         data = Subjects::DataStatisticService.new(subject)
@@ -18,11 +20,9 @@ namespace :subjects do
         next if study_count == 0
         course_study_count = data.course_study_count
         initiative_study = study_count - course_study_count
-        str += ", " unless str.empty?
         str += ("(#{subject.id}, #{study_count}, #{course_study_count}, #{initiative_study}, " +
             "#{data.passed_count}, #{data.course_used_count}, #{data.school_used_count}, " +
             "'#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}', '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}')")
-        buffer_size += 1
         puts "buffer_size: #{buffer_size}; subject_id: #{subject.id}; s: #{s.last}; subject: #{subject == s.last};"
         puts "####str: #{str}"
         if buffer_size == 1000 || subject == s.last