diff --git a/judge/management/commands/generate_data.py b/judge/management/commands/generate_data.py
index 687ccd1..62f9175 100644
--- a/judge/management/commands/generate_data.py
+++ b/judge/management/commands/generate_data.py
@@ -4,41 +4,45 @@ from collections import defaultdict
 import csv
 import os
 from django.conf import settings
+from django.db import connection
 
 
 def gen_submissions():
-    headers = ["uid", "pid"]
-    with open(os.path.join(settings.ML_DATA_PATH, "submissions.csv"), "w") as csvfile:
-        f = csv.writer(csvfile)
-        f.writerow(headers)
-
-        last_pid = defaultdict(int)
-        for u in Profile.objects.all():
-            used = set()
-            print("Processing user", u.id)
-            for s in Submission.objects.filter(user=u).order_by("-date"):
-                if s.problem.id not in used:
-                    used.add(s.problem.id)
-                    f.writerow([u.id, s.problem.id])
-
+    print("Generating submissions")
+    query = """
+    SELECT user_id as uid, problem_id as pid from 
+        (SELECT user_id, problem_id, max(date) as max_date 
+            from judge_submission 
+            group by user_id, problem_id) t 
+            order by user_id, -max_date;
+    """
+    with connection.cursor() as cursor:
+        cursor.execute(query)
+        headers = [i[0] for i in cursor.description]
+        with open(os.path.join(settings.ML_DATA_PATH, "submissions.csv"), "w") as csvfile:
+            f = csv.writer(csvfile)
+            f.writerow(headers)
+            for row in cursor.fetchall():
+                f.writerow(row)
 
 def gen_users():
+    print("Generating users")
     headers = ["uid", "username", "rating", "points"]
     with open(os.path.join(settings.ML_DATA_PATH, "profiles.csv"), "w") as csvfile:
         f = csv.writer(csvfile)
         f.writerow(headers)
 
-        for u in Profile.objects.all():
+        for u in Profile.objects.all().iterator():
             f.writerow([u.id, u.username, u.rating, u.performance_points])
 
 
 def gen_problems():
+    print("Generating problems")
     headers = ["pid", "code", "name", "points", "url"]
     with open(os.path.join(settings.ML_DATA_PATH, "problems.csv"), "w") as csvfile:
         f = csv.writer(csvfile)
         f.writerow(headers)
-
-        for p in Problem.objects.all():
+        for p in Problem.objects.all().iterator():
             f.writerow(
                 [p.id, p.code, p.name, p.points, "lqdoj.edu.vn/problem/" + p.code]
             )