<?php

$dbh = new PDO('firebird:dbname=inet://localhost/employee', 'SYSDBA', 'masterkey');

$dbh->exec('
recreate table t_bug_0001 (
  id bigint not null,
  a int not null,
  b int,
  constraint pk_bug_0001 primary key(id)
)
');

$dbh->exec('recreate sequence g_bug_0001');

$dbh->exec(<<<'SQL'
create or alter trigger t_bug_0001_bi0 for t_bug_0001
active before insert position 0
as
begin
  if (new.id is null) then
    new.id = next value for g_bug_0001;
end
SQL
);

$stmt = $dbh->prepare('insert into t_bug_0001(id, a, b) values(?, ?, ?)');
$stmt->execute([null, 1, 2]);
$stmt->execute([2, 2, null]);
unset($stmt);

$stmt2 = $dbh->prepare('SELECT id, a, b FROM t_bug_0001 WHERE id = ?');

$stmt2->execute([null]); 
$data = $stmt2->fetch(\PDO::FETCH_ASSOC);
$stmt2->closeCursor();
var_dump($data);

$stmt2->execute([2]); 
$data = $stmt2->fetch(\PDO::FETCH_ASSOC);
$stmt2->closeCursor();
var_dump($data);

unset($stmt2);

$dbh->exec('drop table t_bug_0001');
$dbh->exec('drop sequence g_bug_0001');

echo "\nOK\n";