从table1总和总数并将其添加到table2上

I have two tables tblsales and tblproduct. tblsales have | id | pcode | qty| and tblproduct have | id | pcode | pleft | . my question is that I want to total all qty value from tblsales and add it to pleft in tblproduct. I tried what I have learn in MYSQL programming but it doesn't work for me.I have two tables tblsales and tblproduct. tbls