Using volley to retrieve data(multiple rows) from mysql - php

Question

I'm creating a quiz app and i have to retrive all the question to display.this is my php and java code.i'll store the data in another array.i'm not able to fetch any data from my sql table.
StringRequest stringRequest = new StringRequest(Request.Method.POST,insertUrl,
new Response.Listener<String>() {
#Override
public void onResponse(String response) {
try {
jsonArray=new JSONArray(response);
JSONObject jsonObject=jsonArray.getJSONObject(0);
for(int k=0;k<jsonArray.length();k++)
{
question[k]=jsonObject.getString("question");
opta[k]=jsonObject.getString("optionA");
optb[k]=jsonObject.getString("optionB");
optc[k]=jsonObject.getString("optionC");
optd[k]=jsonObject.getString("optionD");
ans[k]=jsonObject.getString("Answers");
}
} catch (JSONException e) {
e.printStackTrace();
}
}
},
new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(Quiz.this,error.toString(),Toast.LENGTH_LONG ).show();
}
}){
#Override
protected Map<String, String> getParams() throws AuthFailureError {
Map<String,String> params = new HashMap<String,String>();
params.put(ITEM_COURSE,data);
return super.getParams();
}
};
RequestQueue requestQueue = Volley.newRequestQueue(this);
requestQueue.add(stringRequest);
This is my php code
<?php
require 'initquiz.php';
global $connect;
$response = array();
$course=$_POST["course"];
$query = "SELECT * FROM questions WHERE course='$course'";
$result= mysqli_query($connect,$query) or die(mysqli_error($connect));
$response= array();
if (mysql_num_rows($result) > 0) {
while ($row = mysql_fetch_array($result)) {
$question = $row[0];
$optionA = $row[2];
$optionB= $row[3];
$optionC = $row[4];
$optionD= $row[5];
$Answers= $row[6];
array_push($response,array("question"=>$question,"optionA"=>$optionA,"optionB"=>$optionB,"optionC"=>$optionC,"optionD"=>$optionD,"Answers"=>$Answers));
}
}
echo json_encode($response);
?>

Answer 1

Issues with your code:
You mixed mysql_* and mysqli_* extension
Your code is vulnerable to SQL injection, use prepared statements
Your fetch could be much simpler
Try to avoid SELECT *, instead select specific fields
Try this approach:
$response = [];
if(isset( $_POST["course"])){
$mysqli = new mysqli("host", "user", "password", "db");
if ($mysqli->connect_errno) {
printf("Connect failed: %s\n", $mysqli->connect_error);
exit();
}
$query = "SELECT * FROM questions WHERE course = ?";
if ($stmt = $mysqli->prepare($query)) {
$stmt->bind_param("s", $_POST["course"]);
$stmt->execute();
while ($row = $stmt->fetch_assoc()) {
$response['data'][] = $row;
}
$response['success'] = true;
}
$mysqli->close();
}else{
$response['data'] = 'No Course Sent';
$response['success'] = false;
}
echo json_encode($response);