/**
  only update columns when values not empty
	update `task` set start = DATE_ADD(start,interval -1 year)
 */

UPDATE 
 `task` 
 
SET 
	 
	`start` = CASE WHEN :start <> '' THEN :start ELSE `start` END,  
	 
 	`id_user` = CASE WHEN :id_user <> '' THEN :id_user ELSE `id_user` END  

WHERE 
 `ID` = :ID
