PDO bindParam behaving strangely

Question

I am having a problem getting PDO bindParam to work correctly. Using this code:

$foo = "bar";

$stmt_1 = $db->prepare("SELECT * FROM table WHERE foo = $foo");
$stmt_1->execute();
$results_1 = $stmt_1->fetchAll();

$stmt_2 = $db->prepare("SELECT * FROM table WHERE foo = ?");
$stmt_2->bindParam(1, $foo, PDO::PARAM_STR);
$stmt_2->execute();
$results_2 = $stmt_2->fetchAll();

$stmt_3 = $db->prepare("SELECT * FROM table WHERE foo = :foo");
$stmt_3->bindParam(":foo", $foo, PDO::PARAM_STR);
$stmt_3->execute();
$results_3 = $stmt_3->fetchAll();

$results_1 contains only the row(s) where foo = bar, $results_2 is empty, and $results_3 contains every entry in "table"

bindValue has the exact same problem, too. Anyone know what's going on here or what I'm doing wrong?

Answer 1

I solved my problem. For some reason, the variables I was setting from $_POST weren't available to the internal functions of a class I had defined, so I added a parameter array to the class to hold the bound variables, and now everything works.