JOIN databases from SELECT - mysql

Question

I need a joined (Union like) result from multiple databases on the same databaseserver in one query. Every customer database contains a location table and all customers are listed in the core database.
I don't need a simple join between to different databases. I need the actual joined database name to come from the same query.
I figure something like this.
SELECT customerlist.dbname,customerlist.realname,location.address
FROM core.customerlist
INNER JOIN `customer.dbname`.location
ORDER BY customerlist.realname
I know this won't work, I'm just trying to pseudo code what I'm searching for. I hope someone can help.
Database structure:
-- Database: `core`
CREATE TABLE IF NOT EXISTS `customerlist` (
`realname` varchar(20) NOT NULL,
`dbname` varchar(16) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `customerlist` (`realname`, `dbname`) VALUES
('Johnny', 'johnny'),
('Alfred', 'alfred');
-- --------------------------------------------------------
-- Database: `alfred`
CREATE TABLE IF NOT EXISTS `location` (
`address` varchar(20) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `location` (`address`) VALUES
('House Three'),
('Car 1');
-- --------------------------------------------------------
-- Database: `johnny`
CREATE TABLE IF NOT EXISTS `location` (
`address` varchar(20) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `location` (`address`) VALUES
('House One'),
('House Two');
Desired result;
johnny,Johnny,House One
johnny,Johnny,House Two
alfred,Alfred,House Three
alfred,Alfred,Car 1

Answer 1

You'll have to be careful of the two table identical tables...joining them in a union if fine since they are identical in structure:
SELECT customerlist.dbname,customerlist.realname,location.address
FROM core.customerlist
LEFT JOIN (
SELECT * FROM (johnny.location UNION alfred.location
)) AS T2 ON customerlist.dbname = T2.dbname
ORDER BY customerlist.realname