Multiple prepared statements with MYSQLI - php

Question

I just moved to mysqli and I was wondering: can I do a multiple query with the prepared statements?
Here is the example: I need to check if this username is also in the table "future_user" and not just in "user" as it is doing right now. For code appeal I'd rather not write again the same function just changing "user" with "future_user".
function isFreeUsername($string)
{
$DB = databaseConnect();
$stmt = $DB->prepare("SELECT * FROM user WHERE username=? LIMIT 1");
$stmt->bind_param("s", $username);
if(isset($_SESSION) && isset($_GET['username'])) $username = $_GET['username'];
else $username = $string;
$stmt->execute();
$stmt->store_result();
if($stmt->num_rows > 0) $return = 0;
else $return = 1;
$stmt->close();
$DB->close();
return $return;
}
TABLES:
CREATE TABLE user
(
uid mediumint(6) unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
username varchar(15) NOT NULL,
password varchar(15) BINARY NOT NULL,
mail varchar(50) NOT NULL,
name varchar(50) NOT NULL,
surname varchar(50) NOT NULL,
birth char(10) NOT NULL,
sex tinyint(1) unsigned NOT NULL default 1,
address varchar(50) NOT NULL,
city varchar(50) NOT NULL,
zip char(5) NOT NULL,
province varchar(50) NOT NULL,
country tinyint(3) NOT NULL,
number1 varchar(50) NOT NULL,
number2 varchar(50) NOT NULL,
last_login TIMESTAMP,
registered TIMESTAMP,
online tinyint(1) unsigned default 0,
admin tinyint(1) unsigned default 0,
comment_allowed tinyint(1) unsigned default 0,
post_allowed tinyint(1) unsigned default 0
) ENGINE=InnoDB;
CREATE TABLE future_user
(
username varchar(15) NOT NULL,
password varchar(15) BINARY NOT NULL,
mail varchar(50) NOT NULL,
name varchar(50) NOT NULL,
surname varchar(50) NOT NULL,
birth char(8) NOT NULL,
sex tinyint(1) unsigned NOT NULL,
address varchar(50) NOT NULL,
city varchar(50) NOT NULL,
zip char(10) NOT NULL,
province varchar(50) NOT NULL,
country varchar(50) NOT NULL,
number1 varchar(50) NOT NULL,
number2 varchar(50) NOT NULL,
code char(10) NOT NULL
) ENGINE=InnoDB;

Answer 1

"SELECT *
FROM user u
LEFT JOIN future_user fu on fu.id = u.id
WHERE u.username=?
LIMIT 1"
With out seeing more of your table structure this what i can come up with.
This will select the user in future user too

Answer 2

You could do a CROSS JOIN to connect the two tables and query them that way
SELECT * FROM user JOIN future_user
WHERE user.username = ? OR future_user.username = ?
You'll probably need to tweak that * so that identically named columns in the two tables don't overlay each other.