根据其他列的数量创建列

I'd like to ask if it's possible to create a column to have content based on the number of other columns, in MySQL server.

By example, column name: count, it's content should be the number of other columns that have the same id:

table members: column id and count
table two: column id and others

Is it possible to store in member.count the number of columns in table two that have the same id than members.id?

If not, I need to create a php function that counts the tables and store the value in members.count, like:

// this should be a for() for every user id
// select all id from members

if ($stmt = $mysqli->prepare("SELECT COUNT(*) rowCount FROM t2 WHERE id = ?")) {
    $stmt->bind_param('ii', $user_id);
    $stmt->execute();
    $stmt->bind_result($rowCount);
    if ($stmt->fetch()) {
        $number_of_rows = $rowCount; // I'm not sure if this variable will store once the stament is closed.
        $stmt->close();
        $stmt = $mysqli->prepare("UPDATE members SET count = ? WHERE id = ?");
        $stmt->bind_param('ii', $number_of_rows, $user_id);
if (! $insert_stmt->execute()) {
    header('Location: /error?err=Registration failure: Contacte al administrador.');
}

    }

I'm not really sure, how can I do this, if the first way it's not possible, I'd appreciate some help finishing this function.

Thanks in advance!