PHP mySQL check if username and password are in the database

Question

I want my code to check if the username and password exist in my database. It does work hardcoded, but I want to do it with a database.Right now this is what I have:

Answer 1

 error_reporting(E_ALL);  
ini_set('display_errors', 1);
session_start();
if(count($_POST)>0) 
{
    include'includePhp.php';
    $sql="SELECT * FROM admin WHERE username='" . $_POST['username'] . "' AND password = '". $_POST['password']."'";
    $result = $con->query($sql);
if ($result->num_rows > 0) 
    {
  while($row = $result->fetch_assoc()) 
            {
        if(!empty($row) && !empty($row['username']) AND !empty($row['password']))
            {
                $_SESSION['username'] = $row['username'];
                echo "SUCCESSFULLY LOGIN ";
                header("Location: inDhanush.php");
            }
        else 
        {
        echo "Try again";
        }
    }
}

}