diff --git a/loop/migration.py b/loop/migration.py
index 3cc9501..3527499 100644
--- a/loop/migration.py
+++ b/loop/migration.py
@@ -1,10 +1,10 @@
-import loop.tables as tables
+import loop.schema as schema
 import loop.habits as habits
 import loop.repetitions as rep
 
 
 def migrate(trackers, events):
-    db = tables.migrate("output.db")
+    db = schema.migrate("output.db")
     if trackers is not None:
 
         habitlist = habits.migrate(db, trackers)
diff --git a/loop/tables.py b/loop/schema.py
similarity index 90%
rename from loop/tables.py
rename to loop/schema.py
index fd5788c..fc6c03c 100644
--- a/loop/tables.py
+++ b/loop/schema.py
@@ -55,7 +55,17 @@ def create_tables(db):
     )
 
 
+def create_constraints(db):
+    c = db.cursor()
+    c.execute(
+        """ CREATE UNIQUE INDEX IF NOT EXISTS idx_repetitions_habit_timestamp 
+            on Repetitions( habit, timestamp);
+        """
+    )
+
+
 def migrate(name):
     db = create_database(name)
     create_tables(db)
+    create_constraints(db)
     return db