Connecting two database in single PHP file

Question

I tried to connect two databases in single php file and tried to retrieve data by joining tables of both databases. Here is my code

require_once "connect.php";

require_once "connect_college.php";

$sql = "select * from college_db.students join mini-project.exam on students.adno=exam.adno and students.receipt=exam.receipt ";

 if (!mysql_query($sql))
              {

               die('Error');
              }
              else
            { 

              header("Location: generate.php"); 
              exit();
            }

Mysql query is not running. college_db and mini-project are the two databases.

Answer 1

Try like

$sql = "select college_db.students.*,mini-project.exam.* from college_db.students 
        join mini-project.exam 
        on college_db.students.adno=mini-project.exam.adno 
        and college_db.students.receipt=mini-project.exam.receipt ";

Answer 2

If to do like this? Not will work?

 $link1 = mysql_connect('localhost', 'mysql_user', 'mysql_password');


 $link2 = mysql_connect('localhost2', 'mysql_user2', 'mysql_password2');

 mysql_select_db('database1', $link1);

 mysql_select_db('database2', $link2);

 $res1=mysql_query($query1,$link1);

 $res2=mysql_query($query1,$link2);