与2个或更多数据库连接，查询和同时

im trying to open a connection with 4 databases (same host). all 4 looks same.

here's my code, but i get no output. why? anyone has a solution? maybe my query is not correct?

thank you!

 <?php 

 $db = new mysqli("localhost","username","password");

 mysqli_select_db('database1', $db); 
 mysqli_select_db('database2', $db); 
 mysqli_select_db('database3', $db); 
 mysqli_select_db('database4', $db); 


 $query = "SELECT A.name AS name1, 
                  B.name AS name2, 
                  C.name AS name3, 
                  D.name AS name4 
        FROM database1.table1 A, 
             database2.table2 B, 
             database3.table3 C, 
             database4.table4 D"; 
 $result = $db->query($query);

 while($row = $result->fetch_assoc()) {

 echo $row['name1'];
 echo $row['name2'];
 echo $row['name3'];
 echo $row['name4'];
 } 

?> 

ok. i have my solution. One connection, only the query... ! thanks for the hints guys!

$query = "
SELECT database1.table1.name as name FROM database1.table1
UNION ALL
SELECT database2.table2.name as name FROM database2.table2
UNION ALL
SELECT database3.table3.name as name FROM database3.table3
UNION ALL
SELECT database4.table4.name as name FROM database4.table4 order by name";