Try below code:
$conn = mysql_connect("hostname","username","password");
mysql_select_db("db1",$conn);
mysql_select_db("db2",$conn);
$query1 = "SELECT * FROM db1.table";
$query2 = "SELECT * FROM db2.table";
You can fetch data of above query from both database as below
$rs = mysql_query($query1);
while($row = mysql_fetch_assoc($rs)) {
$data1[] = $row;
}
$rs = mysql_query($query2);
while($row = mysql_fetch_assoc($rs)) {
$data2[] = $row;
}
print_r($data1);
print_r($data2);