How To Select an Exiting Database? - MySQL FAQs - PHP Connections and Query Execution

The first thing after you have created a connection object to the MySQL server is to select the database where your tables are located, by using the mysql_select_db() function. If your MySQL server is offered by your Web hosting company, they will assign a empty database to you and provide you the database name. You should use this name to select this empty database as your current database. The following script shows you how to select a database called "fyi". It also shows you how to put all the database connection statements in a single include file, and re-use it in all of your PHP pages.

Create the include file, connect.php, with the following statements:

<?php
  $server = "localhost";
  $username = "dev";
  $password = "iyf";
  $database = "fyi";
  $con = mysql_connect($server, $username, $password);
  mysql_select_db($database, $con);
?>

To test this database connection and selection include file, try the following script:

<?php
  include "mysql_connection.php";
  $sql = 'SHOW TABLES';
  if ($rs = mysql_query($sql, $con)) {
    print(mysql_num_rows($rs) . " tables in the database.\n");
  } else {
    print("SHOW TABLES failed.\n");
  }
  mysql_close($con); 
?>

You will get something like this:

0 tables in the database.