How to get constant string array field into db_query?
Not sure if this is a bug or not (I've seen weird things with single and double quote in PDO queries before), but either way you can work around it by using single quotes to wrap the expression:

$sql = "SELECT '\'a\',\'b\'' AS FieldStrArray";
$val = db_query($sql)-&gt;fetchField();
// $val == "'a','b'"