MDL-67312 calendar: upgrade step to delete orphaned events

lib/db/upgrade.php

@@ -3798,5 +3798,15 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2019111800.04);
     }
 
+
+    if ($oldversion < 2019111801.02) {
+        // Delete all orphaned subscription events.
+        $select = "subscriptionid IS NOT NULL
+                   AND subscriptionid NOT IN (SELECT id from {event_subscriptions})";
+        $DB->delete_records_select('event', $select);
+
+        upgrade_main_savepoint(true, 2019111801.02);
+    }
+
     return true;
 }

version.php

@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2019111801.01;              // 20191118      = branching date YYYYMMDD - do not modify!
+$version  = 2019111801.02;              // 20191118      = branching date YYYYMMDD - do not modify!
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.
 $release  = '3.8.1+ (Build: 20200117)'; // Human-friendly version name