Dynamic PDO parameter binding issue with WHERE clause - php

Question

I have a search form where users can enter a few pieces of information to search for records in the database. Due to the fact that some of the fields can be left blank, I am dynamically creating the WHERE clause of the query as well as dynamically binding the PDO parameters. Everything works great if the user only fills out 1 field in the search form but if more than 1 field is used then an empty array is returned. Here is my code.
if(count($_POST)>0)
{
//Remove any key that has no value
$data = array_filter($_POST);
//Define array to hold the pieces of the where clause
$where = array();
//loop each of the variable to build the query
foreach($data as $key=>$value)
{
$key = mysql_real_escape_string($key);
//Push values to array
array_push($where, "$key=:$key");
}
//Create the select query
$query = "SELECT application_ID,
student_last_name,
student_first_name,
s.school_name,
DATE_FORMAT(submission_datetime, '%m/%d/%Y %h:%i:%s %p') AS submission_datetime,
aps.name
FROM application a
LEFT JOIN application_status aps ON(aps.status_ID = a.application_status_ID)
LEFT JOIN schools s ON(s.school_ID = a.school_choice)";
//As long as criteria was selected in the search form then add the where clause to the query with user's search criteria
if(!empty($where))
{
$query .= "WHERE ".implode(" AND ", $where);
}
//Add ORDER BY clause to the query
$query .= " ORDER BY application_ID";
$stmt = $conn->prepare($query);
//loop each of the variables to bind parameters
foreach($data as $key=>$value)
{
$value = mysql_real_escape_string($value);
$stmt->bindparam(':'.$key, $value);
}
$stmt->execute();
$result = $stmt->fetchall(PDO::FETCH_ASSOC);
}
When I echo the query everything looks fine and even returns results when run from PHPMyAdmin. Here is the query.
SELECT application_ID,
student_last_name,
student_first_name,
s.school_name,
DATE_FORMAT(submission_datetime, '%m/%d/%Y %h:%i:%s %p') AS submission_datetime,
aps.name
FROM application a
LEFT JOIN application_status aps ON(aps.status_ID = a.application_status_ID)
LEFT JOIN schools s ON(s.school_ID = a.school_choice)
WHERE school_choice=:school_choice AND status_ID=:status_ID
ORDER BY application_ID ASC
When I print_r I get an empty array.
Thanks for any help you can provide.

Answer 1

When you iterate through an array to bind values to the PDO statement you should use bindValue instead of bindParam.
When you say $stmt->bindparam(':'.$key, $value), the query will use the value of the variable $value as it is at the time of the query execution. Value of $value will be the last element of the array.
http://php.net/manual/en/pdostatement.bindvalue.php
I hope this helps.

Answer 2

You are not supposed to use mysql_real_escape_string() with prepared statements. And in fact, this function will not work if you don't have a mysql_connect() initialized, which you don't.
That must be why it all is failing, your calls to mysql_real_escape_string() are returning FALSE for everything.
Also, what makes you think array keys coming from $_POST are safe to be used in your SQL query? You are taking a serious risk of SQL injection here, don't ever do that.