my @array = (10,15,20);
my $where_list = '';

foreach my $index (0..$#array) {
    $where_list .= ($index) ? "and\n" : "where\n";
    $where_list .= "   company_id='$array[$index]'\n";
}

$sql = <<END_SQL;

select 
   comp_name
from
   companies
$where_list

END_SQL

print $sql;