PDO bindColumn and PDO::FETCH_BOUND -- compulsory or optional? - php

Question

In many places in our PHP code, (working with postgres if it matters)
we have stuff like:
$q = "SELECT DISTINCT a.id FROM alarms.current a, entities e, installations i ";
$q .= "WHERE i.\"entityId\"=e.id AND a.installationid=i.id AND ";
$q .= "e.id=".$entityId;
$stmt = $db->query($q);
$stmt->bindColumn("id", $alarmId);
if ($stmt->fetch(PDO::FETCH_ASSOC))
....etc
Now according to my reading of the docs, if you want your variables updated from their bound columns you ought to use PDO::FETCH_BOUND. But we don't, and no-one has complained about the performance as far as I'm aware.
Can anyone throw any light on why this apparently faulty code actually apparently works?

Answer 1

While the example in the PHP documentation for bindColumn uses PDO::FETCH_BOUND, which does suggest that this fetch style is necessary in order to use bindColumn, it does not explicitly state that this is a requirement. It only says
PDOStatement::bindColumn() arranges to have a particular variable bound to a given column in the result-set from a query. Each call to PDOStatement::fetch() or PDOStatement::fetchAll() will update all the variables that are bound to columns.
After some testing I determined that this will occur regardless of the fetch style that is used. I think the fact that the fetch call in your code is not actually fetched into a variable really just means that an associative array is created and assigned to nothing, while the side effect of the fetch populates the $alarmId variable.

Answer 2

Continuing from #DontPanic's comments, here is how I prefer to use bound parameters:
/**
* #param $id
*
* #return array|false
*/
public function retrieveImage($id)
{
$conn = $this->dbh->getInstance('LocalMSSQL');
$stmt = $conn->prepare("SELECT inputType, blob FROM images WHERE id = ?");
$stmt->bindValue(1, $id, PDO::PARAM_INT);
$stmt->execute();
$resultSet = [
'inputType' => null,
'blob' => null,
];
$stmt->bindColumn(1, $resultSet['inputType'], PDO::PARAM_STR);
$stmt->bindColumn(2, $resultSet['blob'], PDO::PARAM_LOB, 0, PDO::SQLSRV_ENCODING_BINARY);
if ($stmt->fetch()) {
return $resultSet;
} else {
return false;
}
}