Bottomless, Endless

Basically it means you cannot retrieve one column at a time, as the first column you retrieve will move the pointer to the end of the data, and as you cannot rewind, the next call to retrieve the second column will return nothing, because you’re already at the end of the data.

Example:

$sql = "SELECT response, response_comment FROM responses";
$stmt = $dbHandle->prepare($sql);
$stmt->execute();
$stats = $stmt->fetchall(pdo::FETCH_COLUMN, 0);

Then if you proceed to fetch the second column… :

$stats = $stmt->fetchall(pdo::FETCH_COLUMN, 1);

… it will return nothing.

You would have to execute the query again before running a second fetchall().

If it had worked, it could have been used to get the 2 columns in 2 arrays, then run an array_combine() to get the columns of the first array as keys and the columns of the second array as values. Too bad.

Source