The formatting of that last "default" line makes it harder than it should be. This solution relies on the amount of whitespace at the start of column definitions.

#!/usr/bin/perl

use strict;
use warnings;

my $tab;
while (<DATA>) {
  if (/create table.+\.(\w+)/) {
    $tab = $1;
  }

  if (/^    (\w+)/) {
    print "$tab.$1\n";
  }
}

__DATA__
create table "metrica".vodafone_capacity_cell_count_week
  (
    nc_id integer,
    cell_id varchar(50) not null ,
    week_of integer not null ,
    busy_hour "informix".utime,
    gsm_tch_cong_pc_range_1 integer,
    gsm_tch_cong_pc_range_2 integer,
    gsm_tch_cong_pc_range_3 integer,
    gsm_sdcch_cong_pc_range_1 integer,
    gsm_sdcch_cong_pc_range_2 integer,
    gsm_sdcch_cong_pc_range_3 integer,
    gsm_sdcch_cong_pc_range_4 integer,
    gsm_hr_tch_util_pc_range_1 integer,
    gsm_hr_tch_util_pc_range_2 integer,
    gsm_hr_tch_util_pc_range_3 integer,
    gsm_hr_tch_util_pc_range_4 integer,
    gsm_hr_tch_util_pc_range_5 integer,
    gprs_cong_pc_range_1 integer,
    gprs_cong_pc_range_2 integer,
    gprs_cong_pc_range_3 integer,
    config_tch integer,
    config_fpdch integer,
    config_trx integer,
    config_layer integer,
    cell_type varchar(25)
        default null
  );
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