my $query = "
SELECT 
    whatever 
FROM 
    mytable 
WHERE 
    SOUNDEX(name) = SOUNDEX(?) 
    AND SOUNDEX(middle) = SOUNDEX(?)
    AND SOUNDEX(surname) = SOUNDEX(?)";

my $sth = $dbh->prepare($query);
$sth->execute>($name, $middle, $surname);
# check if you got any results
# ....

my $combinedquery = "
SELECT 
    whatever 
FROM 
    mytable 
WHERE 
    SOUNDEX(CONCAT(name,middle,surname)) = SOUNDEX(?)";

$sth = $dbh->prepare($combinedquery);
$sth->execute>("$name$middle$surname");