SQLState: 42S22<br>Error Code: 207
Message: [Microsoft][ODBC Driver 11 for SQL Server][SQL Server]Invalid column name 'r'.
SQLState: 42S22<br>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,)]