PHP连接到ORACLE，但无法访问表行

I have installed PHP and ORACLE on windows 7.

Then I connected PHP to ORACLE using PDO, like this:

$tns = "(DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = oradb)
    )
  )";

$db_username = "C##OTO_USER";
$db_password = "oto_user_pass";

try{
    $conn = new PDO('oci:dbname='.$tns.';charset=UTF8',$db_username,$db_password);
}catch(PDOException $e){
    echo ($e->getMessage());
}

After connection, I try to query some table:

$sth = $conn->prepare("SELECT * FROM mytable");
$sth->execute();
if ($sth->errorInfo()[2] === NULL) { // if no error, print returned result
    $res = $sth->fetchAll(PDO::FETCH_ASSOC);
    var_dump($res);

}
else { // if some error, print error message
    echo $sth->errorInfo()[2];
}

Strange, is that query returns empty array, as if there is no rows in "mytable", though there are rows, if run SELECT * FROM mytable in SQL DEVELOPER, returned all rows.

Also, if make error consciously, then PHP PDO returns error, for example try selecting from non existing table "mytable_bla", gives:

OCIStmtExecute: ORA-00942: table or view does not exist (ext\pdo_oci\oci_statement.c:148)

So, PDO connected to ORACLE DB, but don't sees rows from table, when actually there are rows in table.

What may be caused this?

EDIT

I noticed that PDO don't sees new created table rows, but sees renamed table rows.

For example RENAME mytable TO mytable2, then PDO sees rows from mytable2

Try to attach the scheme name to your table name like so:

$sth = $conn->prepare("SELECT * FROM yourSchemeName.mytable");