如果多个用户同时使用此查询，是否可以？

i have tables that looks like this :

=================================      ==========================
              USER                                NOTE
=================================      ==========================
id_u int auto_increment (PK)           id_n int auto_increment (PK)
name varchar(50)                       id_u int (FK)
                                       text varchar(100)
=================================      ==========================

I am curious if this query might cause any problems on a website with a large amount of users.

$query = "INSERT INTO USER VALUES('','john')"; //query
$result = mysql_query($query);
if($result){
    $query = "INSERT INTO NOTE VALUES (LAST_INSERT_ID(),'','abc')";
    $result = mysql_query($query);
    if($result){
        echo "success";
    }else{
        echo "failed";
    }
}else{
    echo "failed";
}

Will it be fine if multiple users use this query at the same time?

When selecting from and inserting into a table at the same time, MySQL creates a temporary table to hold the rows from the SELECT and then inserts those rows into the target table. However, it remains true that you cannot use INSERT INTO t ... SELECT ... FROM t when t is a TEMPORARY table, because TEMPORARY tables cannot be referred to twice in the same statement

reference : http://dev.mysql.com/doc/refman/5.7/en/insert-select.html