How to check if user name exists and match the existing user name UpperCases and LowerCases

Question

Im using the following code to check if username exists, But this script ignores capital letters.

So JAMES is the same as James

Q1:

How do i ensure that the string matches the existing strings(UserNames) in the database as they are and JAMES is not equated to James.

Q2: mysql_real_escape_string

I only want to allow Numbers and Letters, but i want to detect these unwanted CHARS and tell the user that those funny CHARS are not allowed.

Here's my PHP Block of Code

$l = mysql_real_escape_string($_POST['l']);
     if ( $l == ''){
    echo 'Please Enter your desired username.';
} else {
$Result = mysql_query("SELECT * FROM users WHERE uname = '$l'") or die (mysql_error()); 
if (mysql_num_rows($Result) > 0){
     echo '<span style="color:#F00">Sorry this User-Name is already taken, please choose another User-Name</span>';
} else {
    echo '<span style="color:#090">'.$l.' is ok, Please go ahead and fill the form.</span>';
    }
}

NOTES: - I'm aware of my deprecated mysql, i'll sort it out soon.

Answer 1

Q1 - eh? Dunno why you would want to do this but here you go anyway :-D

"SELECT * FROM users WHERE BINARY `uname` = '$l'"

That makes your search case sensitive

Q2 - simplest way is to just regex is

$newString = preg_replace("/[^a-zA-Z0-9]+/", "", $oldStringWithLoadsOfNaughtyStuff);

if($newString !== $oldStringWithLoadsOfNaughtyStuff){
    //naughty characters must be there as strings do not match.
    echo "naughty Naughty - you have enter illegal characters - only letters and numbers please";

}else{

    //all good here

}

Answer 2

Binary collation can be used:

$Result = mysql_query("SELECT * FROM users WHERE uname = '$l' COLLATE utf8_bin;");