Hi please tell me how to use join for more two tables data
$user_source = $this->src('user_source')->query("select id,name from users");
$purchase_source = $this->src('purchase_source')->query("select user_id,item,amount from purchases");
$join = new Join($user_source,$purchase_source,array("id"=>"user_id"));
$join->pipe($this->dataStore('together'));