组合select语句从多个表中获取数据

Question

我尝试组合两个select语句，第一个语句选择用户正在关注的所有用户，第二个语句选择用户的所有注释以及他们所关注的所有其他用户：

$get_user = $user_data['username'];
$get_following = mysqli_query($con, "SELECT * FROM follows WHERE `follower` = '$get_user'");
$query = mysqli_query($con, "SELECT * FROM  posts WHERE username = '$followe' OR username = '$get_user' ORDER BY date_added DESC LIMIT 0,5 ");

我尝试使用以下代码，但只有当用户关注多个人时才会提取一个条目：

$get_following = mysqli_query($con, "SELECT * FROM follows WHERE `follower` = '$get_user'");
$ffg =mysqli_fetch_assoc($get_following);
$ff = $ffg['follower'];
$query = mysqli_query($con, "SELECT * FROM  posts WHERE username = '$ff' OR username = '$get_user' ORDER BY date_added DESC LIMIT 0,5 ");

有人可以帮忙吗？