Parametrized PDO query and `LIMIT` clause - not working

Question

I have query like this:

SELECT imageurl 
FROM entries 
WHERE thumbdl IS NULL 
LIMIT 10;

It works perfectly with PDO and MySQL Workbench (it returns 10 urls as I want).

However I tried to parametrize LIMIT with PDO:

$cnt = 10;
$query = $this->link->prepare("
             SELECT imageurl 
             FROM entries 
             WHERE imgdl is null 
             LIMIT ?
         ");

$query->bindValue(1, $cnt);

$query->execute();

$result = $query->fetchAll(PDO::FETCH_ASSOC);

That returns empty array.

Answer 1

I just tested a bunch of cases. I'm using PHP 5.3.15 on OS X, and querying MySQL 5.6.12.

Any combination works if you set:

$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

All of the following work: you can use either an int or a string; you don't need to use PDO::PARAM_INT.

$stmt = $dbh->prepare("select user from mysql.user limit ?");

$int = intval(1);
$int = '1';

$stmt->bindValue(1, 1);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindValue(1, '1');
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindValue(1, 1, PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindValue(1, '1', PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindParam(1, $int);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindParam(1, $string);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindParam(1, $int, PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindParam(1, $string, PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

You can also forget about bindValue() or bindParam(), and instead pass either an int or a string in an array argument to execute(). This works fine and does the same thing, but using an array is simpler and often more convenient to code.

$stmt = $dbh->prepare("select user from mysql.user limit ?");

$stmt->execute(array($int));
print_r($stmt->fetchAll());

$stmt->execute(array($string));
print_r($stmt->fetchAll());

If you enable emulated prepares, only one combination works: you must use an integer as the parameter and you must specify PDO::PARAM_INT:

$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, true);

$stmt = $dbh->prepare("select user from mysql.user limit ?");

$stmt->bindValue(1, $int, PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

$stmt->bindParam(1, $int, PDO::PARAM_INT);
$stmt->execute();
print_r($stmt->fetchAll());

Passing values to execute() doesn't work if you have emulated prepares enabled.