No getting result from query on host database - php

Question

On my test machine the query for finding a users last_name and id works fine. I cannot figure out why it will not work on my host.
For this table
students(
id VARCHAR(5) NOT NULL,
first_name VARCHAR(20) NOT NULL,
last_name VARCHAR(40) NOT NULL,
grade SMALLINT UNSIGNED NOT NULL,
PRIMARY KEY (id)
);
I run this query and there is no problem.
$sql="SELECT * FROM $tbl_name WHERE last_name ='$myusername' and id ='$mypassword'";
$result = #mysqli_query ($dbc, $sql);
mysqli_close($dbc);
if(!is_object($result) || $result->num_rows != 1)
{
$errors[] = 'No entries found, maybe capitalize your last name.';
}
else
{
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
$_SESSION['username'] = $_POST['username']; //last name
$_SESSION['firstName'] = $row['first_name'] ;
}
On the host though, there is no rows in the result.
However, I ran this set of code and all the entries show up. Why does the query not work?
$sql="SELECT * FROM $tbl_name";
$num_results = mysqli_num_rows($result);
for ($i=0; $i<$num_results; $i++)
{
$row = mysqli_fetch_assoc ($result);
print stripslashes($row['last_name'])." ".stripslashes($row['id']);
}
By the way, the username is a persons last name and their password is their id. I am not that experienced with PHP and MySql, but this logically does not make sense to me.

Answer 1

Should be using mysqli_query.
Just please be sure to change $link with the connection result (of mysqli_connect).
Code:
$sql = "SELECT * FROM $tbl_name";
$result = mysqli_query($link, $sql);
$num_results = mysqli_num_rows($result);
$i = 0;
while ($row = mysqli_fetch_assoc ($result)) {
print stripslashes($row['last_name'])." ".stripslashes($row['id']);
$i++;
}

Answer 2

I am not sure about it, but I think you're using the wrong language for a mysql host, for example the loop isn't supposed to be in SQL language. As far as I know, this looks like C or C++ (it could depend of what kind of database you're currently using).
But what you need to know is that with this query you need to know the exact name and the exact password. Just in case, do this.
The query in SQL language, should be written it as it follow :
SELECT * FROM students WHERE last_name = "ifyouknowit" OR password="ifyouknowit";
You'll be sure to have at least one result, and it would show up the whole concerned lines as you're calling the " * ". So you don't really need a parameter, as the password is supposed to be unique to everyone.. (Theorically).
In another case, try to add one more column and call it USERID or something like this, to set a unique referent number. So you'll be sure not to be confusing between two people having the same name and last name which could happen easily.
Also, be sure to use the write syntax correctly about the name (like the capital letters are important somehow).
And I notice also that you don't have any password column in this table. Where is it stored? In anycase, with this query you'll still have results.
"students(
id VARCHAR(5) NOT NULL,
first_name VARCHAR(20) NOT NULL,
last_name VARCHAR(40) NOT NULL,
grade SMALLINT UNSIGNED NOT NULL,
PRIMARY KEY (id)
);"
You should call the password database from where it's stored. Put more informations about the other tables and then I'll write a complete query for you.

Answer 3

This code was clearing the variables values so nothing was being searched for in the query. I thought this was standard code that should be used, apparently not.
//prohibit sql injection
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);