Fixed #11964 -- Added support for database check constraints.

tests/constraints/models.py

@@ -0,0 +1,15 @@
+from django.db import models
+
+
+class Product(models.Model):
+    name = models.CharField(max_length=255)
+    price = models.IntegerField()
+    discounted_price = models.IntegerField()
+
+    class Meta:
+        constraints = [
+            models.CheckConstraint(
+                models.Q(price__gt=models.F('discounted_price')),
+                'price_gt_discounted_price'
+            )
+        ]