accessing external database

Oddly, I used the search function and it returned zero results, although I’m sure there are many questions about this.

In any case… I want to be able to call an external database from inside a page and/or post. How do I do that?

I tried the following in a page (using ‘allow php in posts and pages’ plugin), and get errors indicating “no database selected”:

[php]

function main_db_login() {
$passwrd='secretpw';
$user='mysitemain';
$db='mysite_main';
$dbcnx = mysql_connect('localhost',$user,$passwrd);
if (!$dbcnx) {
echo '<p>Unable to connect to the WordPress DB at this time.</p>';
exit();
}
}

function contact_db_login(){
$passwrd='secretpw';
$user='mysitecontact';
$db='mysite_contact';
$dbcnx = mysql_connect('localhost',$user,$passwrd);
if (!$dbcnx) {
echo '<p>Unable to connect to the contacts DB at this time.</p>';
exit();
}
}

 function users_db_login(){
$passwrd='secretpw';
$user='mysiteusers';
$db='mysite_users';
$dbcnx = mysql_connect('localhost',$user,$passwrd);
if (!$dbcnx) {
echo '<p>Unable to connect to the users DB at this time.</p>';
exit();
}
}
[/php]

[php]

mysql_close();
contact_db_login();
$dabble=mysql_query("select * from messages");
while($row=mysql_fetch_array($dabble)){
	print_r($row);
}
mysql_close();
echo'closed';

users_db_login();
$dibble=mysql_query("select * from basic");
while($row=mysql_fetch_array($dibble)){
	print_r($row);
}
mysql_close();
echo'closed';
main_db_login();

[/php]

Any help is appreciated.