Cascade delete in many-to-many tables - mysql

Question

Assume a set of mailing lists in which individuals may be members of more than one list. I've set up a join table:
members -> members2lists <- lists
If the user wants to remove a member from one list only, it would seem necessary only to delete the appropriate row in the members2lists table. But how do I specify the cascading so as not to leave them as an orphan if they're a member of only one list? In other words, how do I delete a member if and only if they are a member of solely the list I'm removing them from?
I'm using PHP and mySQL with InnoDB tables.

Answer 1

Thanks David for your response. I've solved the problem this way (I hope the first two functions are self-expanatory):
$memberID = getIDFromMembers($pdo, $email);
$currListID = getIDFromList($pdo, $listname);
// remove record from join table
$sql = 'DELETE FROM `members2lists` WHERE `member_fk` = :member AND `list_fk` = :list';
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':member', $memberID);
$stmt->bindParam(':list', $currListID);
$stmt->execute();
// check if another record exists in the join table for the same member
$sql = 'SELECT `member_fk` FROM `members2lists` WHERE `member_fk` = :member';
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':member', $memberID);
$stmt->execute();
$row = $stmt->fetch();
if($row === false)
{
// there isn't, the member is an orphan, so delete
$sql = 'DELETE FROM `members` WHERE `member_email` = :email';
$stmt = $pdo->prepare($sql);
$stmt->bindParam(':email', $email);
$stmt->execute();
}
I'd be glad of comments from members about ways to improve this code!