How to get data from a different database and save it to another database

Question

I don't know if this problem of mine is possible. Is it? I have a library system. I add and edit new books in the Catalog Database. In other words, the Catalog Database is for adding/editing books only. I have another Database (not table) for Borrowing Books. I want to store these books, which are viewed through Catalog DB, to Borrowing DB.

I have a snippet for getting data from Catalog DB

error_reporting(0);
$con = mysql_connect("localhost","root","");
mysql_select_db("catalog", $con);

$acc_number=$_GET["acc_number"];

$query="select * from branch where acc_number = '$acc_number'";
$result=mysql_query($query);

while ($row = mysql_fetch_array($result)) {
  //echo $row[1];
}
<textarea name="title" disabled><?php echo $row[1];?></textarea>

And a button for the submission (store to borrowing database). If button is clicked, it's where my problem occurs. I just got a blank page after submitting it. Here is my process.php:

$con = mysql_connect("localhost","root","");
mysql_select_db("catalog", $con);

$acc_number = $_POST['acc_number'];
$title = $_POST['title'];

$sql = mysql_query("select * from books where acc_number='$acc_number'");

while($row=mysql_fetch_array($sql)){
  $con = mysql_connect("localhost","root","");
  mysql_select_db("borrowing", $con);

  $query="INSERT INTO borrowers (title) VALUES ('$title')";
  mysql_query($query);
  if($query){
    header("Location:../librarysystem/books.php");
  }
}

Answer 1

You need to create two sql connections, one for each DB. Then simply get the data from one DB (perform operations, if required) and write to the second DB.

Answer 2

You have two approaches for this:

1. Create two separate DB connections and manipulate data there. Passing $conn as connection to MySQL queries will work.
2. Use the same database using different DB prefixes. Say for example, for first DB it should be

mb_ (Manage Books)

and

bb_ (Borrow Books)

If I were at your place, I would have preferred second approach.

Answer 3

First, I suggest that you use MYSQLI or DO since MYSQL is deprecated. These are suggestions not a fix.

Use only one connect function, you don't need two of them just use the same variable $con.

Add some error checks in there to make sure you are connecting properly

$sql = mysql_query("select * from books where acc_number='$acc_number'") or die ("error message here");

For this

$query="INSERT INTO borrowers (title) VALUES ('$title')";
mysql_query($query);
if($query){
    header("Location:../librarysystem/books.php");
    }

Try

$query=mysql_query("INSERT INTO borrowers (title) VALUES ('$title')") or die("Could not insert...");
    if($query){
        header("Location:../librarysystem/books.php");
        }