PDO fetch() returning empty string - php

Question

I am getting very frustrated. I have two functions which have similar "instructions" ie: return values from a users table in the database.
The second one works fine, however the first one is returning an empty value.
Here is the code:
public function ValidateUser($username, $password)
{
$stmt = "SELECT password FROM users WHERE username = :username LIMIT 1";
if(!($grabUser = $this->db->prepare($stmt)))
{
return null;
}
$grabUser->bindParam(":username", $username, PDO::PARAM_STR);
$grabUser->execute();
$data = $grabUser->fetch();
if(count($grabUser->fetchColumn()) <= 0)
{
return null;
}
echo $data['password'].'s';
if(!password_verify($password,$data['password']))
{
return null;
}
return $this->core->encrypt($data['password']);
}
I'm trying to display the $data['password'] on the page just to test whether it returns a value from the database, however it is simply returning empty, whereas the query is returning a column because it passes the
if(count($grabUser->fetchColumn()) <= 0)
{
return null;
}
condition.
The $username and $password variables are both set, so they are no problem.
Just in case you ask, this is the function that does work properly:
public function ValidateFacebookUser($email, $fid)
{
$stmt = "SELECT username, password FROM users WHERE email_address = :email AND connected_fb = '1' AND connected_fb_id = :fb LIMIT 1";
if(!($grabUser = $this->db->prepare($stmt)))
{
return null;
}
$grabUser->bindParam(":email", $email, PDO::PARAM_STR);
$grabUser->bindParam(":fb", $fid, PDO::PARAM_INT);
$grabUser->execute();
$data = $grabUser->fetch();
if(count($grabUser->fetchColumn()) <= 0)
{
return null;
}
return array($data['username'], $this->core->encrypt($data['password']));
}
It does turn the username and password for that case. Why does it not work in the first function?
Thanks.

Answer 1

No, you shouldn't mix up ->fetchColumn and ->fetch and with LIMIT 1.
What happens is that you already ->fetch() the first row. After that invocation of ->fetchColumn(), there's no more row to fetch.
public function ValidateUser($username, $password)
{
$stmt = "SELECT password FROM users WHERE username = :username LIMIT 1";
if(!($grabUser = $this->db->prepare($stmt))) {
return null;
}
$grabUser->bindParam(":username", $username, PDO::PARAM_STR);
$grabUser->execute();
$data = $grabUser->fetch(); // fetch once
// no need to add ->fetchColumn checking
$ret = null;
if(!empty($data['password']) && password_verify($password,$data['password'])) {
$ret = $this->core->encrypt($data['password']);
}
return $ret;
}

Answer 2

Look at the manual for fetchColumn(). You can see that this fetches the next result set. So if you've already called fetch(), there should be no next result set as per your code:
$data = $grabUser->fetch();
if(count($grabUser->fetchColumn()) <= 0)
{
return null;
}
This will always return null with a LIMIT 1 or single row result.