SQLState: 42S22
Error Code: 207
Message: [Microsoft][ODBC Driver 11 for SQL Server][SQL Server]Invalid column name 'r'.
SQLState: 42S22
Error Code: 207
Message: [Microsoft][ODBC Driver 11 for SQL Server][SQL Server]Invalid column name 'u'.
SELECT TOP 20 * FROM (
                    SELECT   CAST(r AS NVARCHAR(255))  +  CAST(r.id AS NVARCHAR(255))   as uniqueid, r.id, r.useridfrom, r.useridto,
					r.subject, r.fullmessage, r.fullmessageformat,
					r.fullmessagehtml, r.smallmessage, r.notification, r.contexturl,
					r.contexturlname, r.timecreated, r.timeuserfromdeleted, r.timeusertodeleted,
					r.component, r.eventtype, r.timeread
                    FROM mdl_message_read r
                    WHERE r.notification = 1 
					AND r.id IN (SELECT messageid FROM mdl_message_popup WHERE isread = 1)
                    AND r.useridto = '2'
			UNION ALL
				SELECT   CAST(u AS NVARCHAR(255))  +  CAST(u.id AS NVARCHAR(255))   as uniqueid, u.id, u.useridfrom, u.useridto,
				u.subject, u.fullmessage, u.fullmessageformat,
				u.fullmessagehtml, u.smallmessage, u.notification, u.contexturl,
				u.contexturlname, u.timecreated, u.timeuserfromdeleted, u.timeusertodeleted,
				u.component, u.eventtype, 0 as timeread 
				FROM mdl_message u
				WHERE u.notification = 1  
				AND u.id IN (SELECT messageid FROM mdl_message_popup WHERE isread = 0) 
				AND u.useridto = '2'
                ) f ORDER BY timecreated DESC, timeread DESC, id DESC[array (  0 => 2,  1 => 2,)]
Error code: dmlreadexception
* line 479 of \lib\dml\moodle_database.php: dml_read_exception thrown
* line 297 of \lib\dml\sqlsrv_native_moodle_database.php: call to moodle_database->query_end()
* line 404 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->query_end()
* line 865 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->do_query()
* line 913 of \lib\dml\sqlsrv_native_moodle_database.php: call to sqlsrv_native_moodle_database->get_recordset_sql()
* line 100 of \message\output\popup\classes\api.php: call to sqlsrv_native_moodle_database->get_records_sql()
* line 111 of \message\output\popup\externallib.php: call to message_popup\api::get_popup_notifications()
* line ? of unknownfile: call to message_popup_external::get_popup_notifications()
* line 229 of \lib\externallib.php: call to call_user_func_array()
* line 59 of \lib\ajax\service.php: call to external_api::call_external_function()