how to query a value and add it to the date - php

Question

I have a problem, you see I borrow a book getting the book_id and the date borrow is set to the date today, but each book has a days_id value that I need to add to the day of the borrow_date now I'm having trouble how can I get that date_id from the book_id I chosen and add it inside my borrow_date so that I can generate my due_date automatically
here is my PHP code
<?php
include 'connect.php';
$librarian_id = $_POST['librarian_id'];
$member_id = $_POST['member_id'];
$book_id = $_POST['book_id'];
$date_borrow = $_POST['date_borrow'];
$status_id = $_POST['status_id'];
$days = "SELECT days_id, book_id FROM book_setup
WHERE book_id = '$book_id' AND days_id = " . $row['book_id'] . " ";
$result = mysqli_query($conn, $days);
$due_date = date('Y-m-d', strtotime($date_borrow. ' + $result days'));
if ($librarian_id == '') {
echo "librarian is empty";
}
else if ($member_id == '') {
echo "member id is empty";
}
else if ($book_id == '') {
echo "book is empty";
}
else if ($date_borrow == '') {
echo "date borrow is empty";
}
else if ($status_id == '') {
echo "status is empty";
}
else if ($due_date == '') {
echo "due date is empty";
}
else {
$sql = " INSERT INTO borrow_book (librarian_id, member_id,
book_id, date_borrow, due_date, status_id)
VALUES
('$librarian_id', '$member_id', '$book_id',
'$date_borrow', '$due_date', '$status_id' ) ";
if ($conn->query($sql) === TRUE)
{
$message = "Borrowing book successful";
echo "<script type='text/javascript'>alert('$message');</script>";
}
else
{
$message = "Borrowing book failed Failed";
echo "<script type='text/javascript'>alert('$message');</script>";
}
}
$conn->close();
?>
and this is my HTML code
<?php
include 'php/header.php';
require_once 'php/connect.php';
?>
<form method="POST" action="php/borrow.php">
<h1>Borrow Book</h1>
Transacted by:
<br>
<div>
<select name="librarian_id">
<option>Select Librarian
<?php
$sql = "SELECT * FROM librarian";
$result = mysqli_query($conn, $sql);
while ($row =mysqli_fetch_assoc($result)) {
echo "<option value='" . $row['librarian_id'] ."'>"
. $row['Fname'] . " " . $row['Lname'] . "</option>";
}
?>
</option>
</select><br><br>
</div>
Select Member
<br>
<div>
<select name="member_id">
<option>Select member
<?php
$sql = "SELECT * FROM members";
$result = mysqli_query($conn, $sql);
while ($row =mysqli_fetch_assoc($result)) {
echo "<option value='" . $row['member_id'] ."'>"
. $row['Fname'] . " " . $row['Lname'] . "</option>";
}
?>
</option>
</select><br><br>
</div>
<div>
<select name="book_id">
<option>Select a Book
<?php
$sql = "SELECT book_setup.book_id, book.book_id, book.title FROM book_setup
INNER JOIN book ON book_setup.book_id = book.book_id WHERE book_setup.status_id = '1' ";
$result = mysqli_query($conn, $sql);
while ($row =mysqli_fetch_assoc($result)) {
echo "<option value='" . $row['book_id'] . "'>"
. $row['title'] . "</option>";
}
?>
</option>
</select><br><br>
</div>
Borrow Date:
<br><br>
<input name="date_borrow" value="<?php echo date('Y-m-d'); ?>" readonly>
<br><br>
Status:
<div>
<select name="status_id">
<option>
<?php
$sql = "SELECT * FROM borrower_status";
$result = mysqli_query($conn, $sql);
while ($row =mysqli_fetch_assoc($result)) {
echo "<option value='" . $row['status_id'] ."'>"
. $row['status'] . "</option>";
}
?>
</option>
</select><br><br>
</div>
<br>
<br>
<button class="button" type="submit">Submit</button>
<button type="reset" value="Reset">Reset</button>
</form>
this is my database for borrowing book
and this is where I get the book that is available to borrow

Answer 1

Do this:
$res = mysqli_query($con, " SELECT days_id FROM book_setup WHERE book_id = '$book_id' ");
$days = mysqli_fetch_assoc($res)['days_id'];