查询中有多个数据库连接

I have 2 databases and i need to make a join from both databases in a query. But how is this possible when you prepare the statement?

I have 2 database connection files. But how for example could i select one table from on database (pdo) and then join from other table in the other database (pdotwo)?

private $pdo;
    private $pdotwo;

    public function __construct(DB $pdo, DBTwo $pdotwo)
    {
        $this->pdo = $pdo->pdo;
        $this->pdotwo = $pdotwo->pdotwo;
    }

This is very similar to an older question on the same topic so see if that answers your needs.

It doesn't deal with the Class structure but deals with the practicalities of the connections.

The main point is that if your databases are on the same host you don't need to prepare two connections, you can simply prepare one connection and then specify the name of the 2nd database in your query:

$db = new PDO('mysql:host=localhost;dbname=db1;charset=utf8', 'username', 'password');

$result = $db->query("
    SELECT *
    FROM   table_on_db1 a, `db2`.`table_on_db2` b
    WHERE  a.id = b.fk_id
");