mysql concat a vložit do nefunguje

Použijte INSERT INTO...SELECT

insert into products(productname,proddescription,supplier,lastpurchasedate,quantityleft)
select concat('PID',pid,pname),pdesc,psupp,pdate,pquant

Sloupec productid můžete vynechat pokud se jedná o AUTO_INCREMENT sloupec.

Zajímalo by mě, proč musíte provést select pid=last_insert_id(); když pid je IN parametr .

AKTUALIZACE 1

DROP PROCEDURE `inserproducts`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `inserproducts`
(
   pid int,
   pname varchar(50),
   pdesc varchar(50),
   psupp varchar(50),
   pdate date,
   pquant int
)
begin

    insert into products
          (productname,
           proddescription,
           supplier,
           lastpurchasedate,
           quantityleft)
    select concat('PID',pid,pname), pdesc, psupp, pdate, pquant;

    select last_insert_id();
end$$
DELIMITER ;