PDOStatement's bindValue only working with value of "0" - php

Question

I'm trying to get data from a MySQL database using PDO. For example, I would run blixUserGetInfo("2767207") if the user's id was 2767207.
But, whenever I run it with a User ID other than 0, blixUserGetInfo("0"), null is returned, and no errors are thrown, even though the supplied ID does exist in the database.
function blixUserGetInfo($userid){
$connection = //database connection
// replacing this with
// "SELECT * FROM `users` WHERE `id` = $userid"
// works for some reason
$statement = "SELECT * FROM `users` WHERE `id` = ?";
$prepared = $connection->prepare($statement);
$prepared->bindValue(1, $userid); //returns TRUE
$prepared->execute(); //also returns TRUE
$code = $prepared->errorCode(); //returns '00000' (no error)
return $prepared->fetch(); //returns null
}
But, If I change $statement from
"SELECT * FROM `users` WHERE `id` = ?"
to
"SELECT * FROM `users` WHERE `id` = $userid"
and remove the bindValue statement, it works as expected.
I've also tried changing the bindValue statement to bindValue(1, $userid, PDO::PARAM_INT), but still have no luck. Both of the times the statement returns true.
Why doesn't the first example work like it should? Is it a bug, am I doing something wrong, or is it expected behavior?

Answer 1

I really dislike this bindValue and bindParam complexity unless it's absolutely necessary. You can simplify your code using parameters for execute
$statement = "SELECT * FROM `users` WHERE `id` = ?";
$prepared = $connection->prepare($statement);
$prepared->execute(array($userid));
While i know this does not answer why bindValue is not working, it takes away having to worry about pass by reference and pass by value stuff which could be a factor in this question.
If this execute does not return an error and your table does have data for that condition than its almost surely going to return it.
Although i didn't confirm it but your act of setting the connection to null before you fetch might be the actual reason you fail to see any data. Why would you set the connection to NULL and try to fetch afterwards ?

Answer 2

I suggest you just not use the bindValue() function anymore.
The bindParam() function works better in this case. Use the value placeholder instead of ?'s (:[placeholder name])
$statement = "SELECT * FROM `users` WHERE `id` = :id";
$prepared = $connection->prepare($statement);
$prepared -> bindParam(":id", $value)
$prepared -> execute();