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

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

WHERE 
 `ID` = :ID
