क्या आपने बनाने की कोशिश की है
$result = mysqli_query($conn,"SELECT * FROM comments ORDER BY id DESC limit '$sqlshowvalue'");
करने के लिए
$result = mysqli_query($conn,"SELECT * FROM comments ORDER BY id DESC limit ".$sqlshowvalue);
क्या आपने बनाने की कोशिश की है
$result = mysqli_query($conn,"SELECT * FROM comments ORDER BY id DESC limit '$sqlshowvalue'");
करने के लिए
$result = mysqli_query($conn,"SELECT * FROM comments ORDER BY id DESC limit ".$sqlshowvalue);