If I try it without the single quotes within the func declaration, I get a strict subs error

Something like this?

#!/bin/env perl
# create a SQLite test database
use strict;
use warnings;
use DBI;

my $db = shift @ARGV || 'no_name.splite';

my $dbh = DBI->connect(
    "dbi:SQLite:$db", "", "",
    {
        RaiseError => 1,
        sqlite_see_if_its_a_number => 1,
        PrintError => 0
    }
);

$dbh->func('sqrt_s_s', -1, \&sqrt_sum_of_sqrs, 'create_function'); # n
+eed length function

my @rowa = $dbh->selectrow_array( "select 3 as A, 4 as B, sqrt_s_s( 3,
+ 4 ) as C" );

print join( "\t", @rowa ), "\n";

sub sqrt_sum_of_sqrs {
    my $sum_sqrs = 0.0;
    map { $sum_sqrs += $_ ** 2 } @_;
    return sqrt( $sum_sqrs );
}
[download]

Update: So now you need to research three things.

1. How would you prompt a user for input?
2. How to get the user input?
3. How do you pass the user input into your function?