SQL: Add ON DELETE CASCADE

that allows deleting data from tables events and sent without manually
deleting the corresponding entries from the directives.

There's no value in blocking the deletion of entries in the table
directives, which are obsolete anyway, when one wants to delete entries
from the events table.

Author: sebix

sql/notifications.sql

@@ -67,8 +67,8 @@ CREATE TABLE directives (
 
     inserted_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
 
-    FOREIGN KEY (events_id) REFERENCES events(id),
-    FOREIGN KEY (sent_id) REFERENCES sent(id)
+    FOREIGN KEY (events_id) REFERENCES events(id) ON DELETE CASCADE,
+    FOREIGN KEY (sent_id) REFERENCES sent(id) ON DELETE CASCADE
 );