diff --git a/backend/src/main/resources/db/migration/V6__sale_cart_unique_constraint.sql b/backend/src/main/resources/db/migration/V6__sale_cart_unique_constraint.sql
new file mode 100644
index 00000000..edfdf34a
--- /dev/null
+++ b/backend/src/main/resources/db/migration/V6__sale_cart_unique_constraint.sql
@@ -0,0 +1 @@
+ALTER TABLE sale ADD CONSTRAINT uq_sale_cart_id UNIQUE (cartId);