php get api

<?php
    $host="localhost"; //replace with database hostname
    $username="username"; //replace with database username
    $password="password"; //replace with database password
    $db_name="db_name"; //replace with database name
    $con=mysql_connect("$host", "$username", "$password")or die("cannot connect");
    mysql_select_db("$db_name")or die("cannot select DB");

    if($_SERVER["REQUEST_METHOD"] == "POST") {
        $matric = $_POST['matric'];
        $sql = "select * from students where `matric` = '$matric'";
    } else {
        $sql = "select * from students";
    }
    $result = mysql_query($sql);
    $json = array();
    if(mysql_num_rows($result)){
        while($row=mysql_fetch_assoc($result)){
            $json['stu_info'][]=$row;
        }
    }
    mysql_close($con);
    echo json_encode($json);
?>