Description:
------------
From the version of FIREBIRD 3.0.0, Boolean type support was introduced (https://www.firebirdsql.org/file/documentation/release_notes/html/en/3_0/rnfb30-ddl-enhance.html#rnfb30-ddl-boolean)

Currently, the PDO returns only null values for Boolean columns

Test script:
---------------
CREATE TABLE TBOOL (ID INT, BVAL BOOLEAN);
COMMIT;

INSERT INTO TBOOL VALUES (1, TRUE);
INSERT INTO TBOOL VALUES (2, 2 = 4);
INSERT INTO TBOOL VALUES (3, NULL = 1);
COMMIT;

<php
$pdo = new \PDO('firebird:dbname=localhost:/tmp/TEST.FDB', 'SYSDBA', 'masterkey', array(
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_CASE    => PDO::CASE_LOWER,
        ));

$stmt = $pdo->prepare("SELECT * FROM TBOOL");
$stmt->execute();
$rows = $stmt->fetchAll();
var_dump($rows);


Expected result:
----------------
          ID    BVAL
============ =======
           1 <true>
           2 <false>
           3 <null>

Actual result:
--------------
          ID    BVAL
============ =======
           1 <null>
           2 <null>
           3 <null>