PDO::NULL_EMPTY_STRING: Empty string is converted to NULL.
PDO::NULL_TO_STRING: NULL is converted to an empty string.
PDO::ATTR_STRINGIFY_FETCHES: Convert numeric values to strings when fetching. Requires bool.
PDO::ATTR_STATEMENT_CLASS: Set user-supplied statement class derived from PDOStatement. Cannot be used with persistent PDO instances. Requires array(string classname, array(mixed constructor_args)).
PDO::ATTR_AUTOCOMMIT (available in OCI, Firebird and MySQL): Whether to autocommit every single statement.
PDO::MYSQL_ATTR_USE_BUFFERED_QUERY (available in MySQL): Use buffered queries.