Compare values in two tables with php and Mysqli

I have to compare if the numbers in table A exist in table B being that if there is one statement but another one. I tried this and it did not work, it does not return anything else.

Note: Table B may not have codigo of table A

EXAMPLE:

TABELA A campo => (codigo): 12,13,23,44,55
TABELA B campo => (meucampo): 13,44,55


$sql_A="SELECT * FROM A"; 
$resultado_A = $conexao->query($sql_A);
while($row_A = $resultado_A->fetch_assoc()) : ?>


    $sql_B="SELECT * FROM B WHERE meucampo = ".$row_A['codigo']." "; 
    $resultado_B = $conexao->query($sql_B);

        while($row_B = $resultado_B->fetch_assoc()) :

            if($row_A['codigo'] == $row_b['meucampo'])  :
                echo"<a href='link'>foo</a>";
                else   :
                echo"<a href='link'>foo/bar</a>";

            endif;

        endwhile; 

endwhile;