allow only specified users to access a page - php

Question

I'm having issues with making a page where only band members can access their own band pages.
Each band in my band table has four columns $bandm1 $bandm2 $bandm3 and $bandm4.
I tried to make a script that drew the session username, and then drew the band_id from the url, and that was successful. but when i tried:
the script didn't work. is it a problem with my AND/OR statements?
EDIT:
here's my full code:
$user = $_SESSION['user_name'];
$get_user = "
select *
from users
where user_name = '$user'
";
$run_user = mysqli_query($con,$get_user);
$row=mysqli_fetch_array($run_user);
$user_name = $row['user_name'];
if(isset($_GET['band_id'])) {
$band_id = mysqli_real_escape_string($con, $_GET['band_id']);
if (ctype_alnum($band_id)){
$q = "SELECT * FROM bands WHERE band_id = '$band_id' ";
$r = mysqli_query($con, $q);
if($r){
while($row=mysqli_fetch_array($r)){
$band_id = $row['band_id'];
$band_name = $row['band_name'];
}
}
}
?>
FROM bands
WHERE band_id = '$band_id'
and (bandm1 = $user_name) OR (bandm2 = $user_name)
OR (bandm3 = $user_name) OR (bandm4 = $user_name)
it works, BUT when i replace the select with:
SELECT * FROM bands WHERE band_id = '$band_id' and (bandm1 = $user_name) OR (bandm2 = $user_name) OR (bandm3 = $user_name) OR (bandm4 = $user_name)";
it stops working

Answer 1

Try adding parentheses to your query:
SELECT * FROM bands WHERE band_id = '$band_id' and ( (bandm1 = $user_name) OR (bandm2 = $user_name) OR (bandm3 = $user_name) OR (bandm4 = $user_name) )
Edit :
You probably need some quotes around these variables, not sure how your script is built, but something like this :
$query = "SELECT * FROM bands WHERE band_id = '".$band_id."' and ( bandm1 = '".$user_name."' OR bandm2 = '".$user_name."' OR bandm3 = '".$user_name."' OR bandm4 = '".$user_name."' )";