MYSQLI prepared statement proceeds no output

Question

I've just started learning MYSQLI prepared statements technique and faced really annoying issue. My code stops at bind_result(). And I just don't get it what could be wrong, so please, guys, help me.

Here is my config.php:

 <?php 
  $db_name = 'site'; 
  $db_user = 'root'; 
  $db_pass = 'root'; 
  $db_host = 'localhost';
  $db_port = 8889;

  $db = new mysqli($db_host, $db_user, $db_pass, $db_name, $db_port);

  if($db->connect_errno > 0){
  die('Unable to connect to database [' . $db->connect_error . ']');
  }
 ?>

And my main code:

 <?php
  include 'config.php';
  $post_id=450;
  $stmt = $db->prepare("SELECT * FROM messages WHERE post_id = ?");
  if ( false===$stmt ) {
  die('prepare() failed: ' . htmlspecialchars($db->error));
  }
  $ex=$stmt->bind_param('i', $post_id); // Bind "$post_id" to parameter.
  if ( false===$ex ) {
  die('bind_param() failed: ' . htmlspecialchars($stmt->error));
  }
  $ex=$stmt->execute();// Execute the prepared query.
  if ( false===$ex ) {
  die('execute() failed: ' . htmlspecialchars($stmt->error));
  }
  $ex=$stmt->store_result();
  if ( false===$ex ) {
  die('store_result() failed: ' . htmlspecialchars($stmt->error));
  } 
  $ex=$stmt->bind_result($p); 
  if ( false===$ex ) {
  die('bind_result() failed: ' . htmlspecialchars($stmt->error));
  }
  while($stmt->fetch()){
  echo $p;
  }

 ?>

Answer 1

Here is how your config.php have to be

<?php 
error_reporting(E_ALL);
ini_set('display_errors', 1); // change it to 0 on production server

$db_name = 'site'; 
$db_user = 'root'; 
$db_pass = 'root'; 
$db_host = 'localhost';
$db_port = 8889;

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$db = new mysqli($db_host, $db_user, $db_pass, $db_name, $db_port);

and here is how your main code have to be

<?php
include 'config.php';
$post_id=450;
$stmt = $db->prepare("SELECT * FROM messages WHERE post_id = ?");
$stmt->bind_param('i', $post_id);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($p); // here is where an error have to be shown
while($stmt->fetch()){
  echo $p;
}

Answer 2

Your initial problem is that you weren't checking every call for failure, just the few at the start. Both store_result and bind_result can also fail.

Your specific problem (once you've fixed the initial one) is that you're doing select * to get multiple columns but you're only binding one in the result. That's evident from the error message you get from the bind_result call:

Number of bind variables doesn't match number of fields

If you change the select statement to something like select id from ... , you'll find it starts working.

However, assuming you want more columns, you should provide more variables in the binding, something like:

$stmt = $db->prepare("SELECT col1, col2 FROM messages WHERE post_id = ?");
:
$ex = $stmt->bind_result($param1, $param2);

You'll notice I'm not using select * up there, it's better to use explicit column naming in almost all situations so that:

• you don't get surprised when the DB schema changes;
• you only get the data you need;
• you can map columns to result variables properly.

Pretty much the only place I've ever found it's okay to use select * is in DB analysis tools where you want to get everything. If you know what you want in advance, that's what you should ask for.

Answer 3

Make sure that your error reporting is turned on by adding the following code at the top of your page before include 'config.php' :

error_reporting(E_ALL);

then you can diagnose it to find out where is the error comming from.