MySql error : Result consisted of more than one row - php

Question

I have the error : Result consisted of more than one row but i can't find out it.
The entry id_user has only one record in its table.
The procedure:
CREATE DEFINER=`root`#`localhost` PROCEDURE `delete_user_deep`(id_user int(11))
BEGIN
declare nome_loc varchar(45);
declare cognome_loc varchar(45);
select nome,cognome
into nome_loc,cognome_loc
from user
where id_user=id_user;
delete from Radius.radcheck where username in (
select mac_address from machine where id_user =id_user);
delete from Radius.radreply where username in (
select mac_address from machine where id_user =id_user);
delete from machine_ip where id_machine in (
select id_machine from machine where id_user=id_user);
delete from machine where id_user = id_user;
delete from document where id_user=id_user;
delete from user where id_user=id_user;
insert into log_generic values(
NULL,
'USER',
'Delete User Deep',
(select concat ('User: ',id_user,' Name: ',cognome_loc,' Prename: ',nome_loc)),
now());
END

Answer 1

The problem is in this statement:
select nome,cognome
into nome_loc,cognome_loc
from user
where id_user=id_user;
This will return an error if there is more than one row. The error is documented here.
This is caused because the parameter name is the same as the column name. The id_user is referring to the column on both sides of the comparison.
The query should look like:
select nome, cognome
into nome_loc, cognome_loc
from user
where id_user = param_id_user;
Always prefix parameter and variable names with something to distinguish them from column names.