Passing array of values from form to sql query WHERE IN clause

Question

I have a form with a number of checkboxes, which are generated from unique values in a MySQL table:

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
<?php
    $query5="SELECT distinct from_user from tracks WHERE uploaded_page='$this_path_short' ORDER BY from_user";
    $result5=mysql_query($query5) or die(mysql_error());
    while ($row = mysql_fetch_array($result5)) {
        $from_user = $row['from_user'];
        echo "<input type=\"checkbox\" name=\"from_user[]\" value=\"AND ".$from_user."\" checked=\"checked\">".$from_user."<br>";
    }
?>
<input type="submit" name="submit" value="filter"><br>

I would then like to pass the array of 'from_user' values to another MySQL query on the page. I can get the values like this:

$names=implode(" ", $_POST['from_user']);

But I am not sure how to include this array in the following MySQL query:

$query1="SELECT * FROM tracks WHERE from_user IN **array goes here**)";

Answer 1

$query1='SELECT * FROM tracks WHERE from_user IN ('.implode(',',$_POST['from_user']).')';

Answer 2

Remove the AND so the checkbox value looks like this:

echo "<input type=\"checkbox\" name=\"from_user[]\" value=\"".$from_user."\" checked=\"checked\">".$from_user."<br>";
    }

IN expects comma separated values:

$names=implode(",", $_POST['from_user']);    
$query1="SELECT * FROM tracks WHERE from_user IN (".$names."))";

!!!! BUT: Please, please, please use prepared statements because your code is wide open to SQL Injection: http://php.net/manual/de/mysqli.prepare.php

$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
  printf("Connect failed: %s\n", mysqli_connect_error());
  exit();
}

$result = null;
$names = implode(",", $_POST['from_user']);  

/* create a prepared statement */
if ($stmt = $mysqli->prepare("SELECT * FROM tracks WHERE from_user IN (?)")) {

  /* bind parameters for markers */
  $stmt->bind_param("s", $names);

  /* execute query */
  $stmt->execute();

  /* bind result variables */
  $stmt->bind_result($result);

  /* fetch value */
  $stmt->fetch();

  print_r($result);

  /* close statement */
  $stmt->close();
}

/* close connection */
$mysqli->close();