Index: openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.10.0d2-5.10.0d3.sql
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.10.0d2-5.10.0d3.sql,v
diff -u -N -r1.1 -r1.2
--- openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.10.0d2-5.10.0d3.sql	3 Oct 2018 09:11:50 -0000	1.1
+++ openacs-4/packages/notifications/sql/postgresql/upgrade/upgrade-5.10.0d2-5.10.0d3.sql	2 Nov 2018 09:37:30 -0000	1.2
@@ -1,4 +1,25 @@
+--
+-- Delete from duplicated notification request entries, which are
+-- entries having duplicate values in the columns (type_id, user_id,
+-- object_id).
+--
+WITH dups AS (                                                                                                                     
+   select n.* from notification_requests n, (
+      select type_id, object_id, user_id, count(*) from notification_requests group by 1, 2, 3 HAVING count(*) > 1
+      ) d where n.type_id = d.type_id and n.object_id = d.object_id and n.user_id = d.user_id
+)
+DELETE FROM notification_requests a USING dups b
+WHERE a.request_id < b.request_id
+and a.type_id = b.type_id and a.object_id = b.object_id and a.user_id = b.user_id;
 
+--
+-- Allow to run this script multiple times.
+--
+ALTER TABLE notification_requests DROP CONSTRAINT IF EXISTS notification_requests_un;
+
+--
+-- Add the real constraint.
+--
 ALTER TABLE notification_requests
 ADD CONSTRAINT notification_requests_un
 UNIQUE (type_id, user_id, object_id);