too long

$con = mysql_connect("localhost","username","password","db name") or die('not connected');
echo "connected";

$sql = "SELECT id, first_name, last_name FROM reg-users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
// output data of each row
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["first_name"]. " " . $row["last_name"]. "<br>";
    }
}
else 
{
    echo "0 results";
}   

I have used above code. But not working. mysql select query is not working. Please give me solution.

Change the following line of code

$result = $conn->query($sql);

with

$result = $con->query($sql);

As you have $con as mysql connection object.

And also try to learn basic select queries from http://www.tutorialspoint.com/

Do the following changes in the code:

1. Replace mysql_connect() to mysqli_connect()
2. Replace the line $result = $conn->query($sql); with $result = $con->query($sql); <<-- please note spelling mistake in $con

Your code should be:

$con = mysqli_connect("localhost","username","password","db name") or die('not connected');
echo "connected";

$sql = "SELECT id, first_name, last_name FROM reg-users";
$result = $con->query($sql); // <<-- please note spelling mistake in $con

if ($result->num_rows > 0) {
// output data of each row
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["first_name"]. " " . $row["last_name"]. "<br>";
    }
}
else 
{
    echo "0 results";
}