Retrieve a table from DB using php and then choose a specific item

let me assume you have a these rows in the table book book_id(PI), name author

<form method="post" action="something.php">
<select name="book">
<?php
$stmt = $mysqli->prepare("SELECT id,name,author FROM books");
if($stmt) {
$stmt->execute();
$result = $stmt->get_result();
while ($myrow = $result->fetch_assoc()) {
echo '<option value='.$myrow['book_id'].'>'.$name.' '.$author.'</option>';
}
//instead of $result you can also do
if($stmt) {
$stmt->execute();
$stmt->bind_result($id,$name,$author):
while ($stmt->fetch()) {
echo '<option...
}
?>

if you want both the id and name or all of the three go to this link

if you want to select your books on certain criteria, for example lets say author=enid

then modify the query like this:

$stmt = $mysqli->prepare("SELECT id,name,author FROM books WHERE author=?");
if($stmt) {
$stmt->bind_param("s",$input_name);
$stmt->execute();
.....

then at the something.php use the $_POST[''] to get the user inputs. then u can make a form use a hidden value with a value= id of the book make a comment box use a submit button. then in another table 'comments' u can have two rows comment_id(PI) book_id and comment

then use the insert query

$stmt=mysqli_prepare("insert into comments (book_id,comment) values (?,?)");
if($stmt) {
 $stmt->bind_param('is',$book_id,$comment);
$stmt->execute();
}

always remember to use $stmt->close() and $stmt->free() . how to do that will be answred by php.net