package SQL_Helpers;

my %sql_statements = ( 
    SELECT_USER_INFO => q/SELECT userid, username, password FROM user_table WHERE userid=?/,
    UPDATE_USER_INFO => q/UPDATE user_table set password=? WHERE userid=?/,
    ...yada yada yada...
    );

sub sql {
    my ( $dbh, $sql, @data ) = @_;
    return undef if !exists( $sql_statements{ $sql } );
    my $sth = $dbh->prepare( $sql_statements{ $sql } )
        or die DBI::errstr;
    $sth->execute( @data ) or die DBI::errstr;
    return $sth;
}

...

package MyPackage;
use SQL_Helpers qw/:all/;

my $sth = sql( $dbh, UPDATE_USER_INFO, $password, $userid );