Mysqli - When opening 2 connections to the same host with mysql, but different databases, does mysqli open the connection once?

Question

When I have a situation like this:

$databaseA = new mysqli($host,$user,$pass,\"databaseA\");
$databaseB = new mysqli($host,$user,$pass,\"databaseB\");


        

Answer 1

For every mysqli-object there will be a separate connection.

Try a

SHOW FULL PROCESSLIST; 

on your MySQL server during runtime, you'll see two different processes connected from the same host if your example is implemented.

Answer 2

Assuming you have a good reason to use two different databases, the only way to make this work with a single connection is with a user that has privileges to access both databases. It would go something like this:

$db = new mysqli($host,$user,$pass); // connect to the MySQL server without specifying a database

mysqli_select_db('databaseA', $db); // Specify your default/most-used database

If you don't explicitly specify databaseB in your query, MySQL will use the default (databaseA). So a query that gets one column from databaseB and two from databaseA would look like this:

$query = "SELECT databaseB.table.column, table.column, table.column2";