my %hash = map { 
                    join(':', $_->{Computer}, 
                              $_->{Bulletin}, 
                              ( $_->{Product} || "" ), 
                              $_->{Status} 
                    ) => $_ 
                } @{GetQueryTable('all_records_for_report', 138)};
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or

my %hash;
for ( @{GetQueryTable('all_records_for_report', 137)} ) {
    $hash{"$_->{Computer}:$_->{Bulletin}:"
            . ($_->{Product}||"") 
            . ":$_->{Status}"} = $_;
}
[download]

Well, the map-based approach puts the focus on the fact that you're populating %hash. Where you're getting the data from is secondary. The for-based approach puts the focus on the fact that you're doing something with each element in all_records_for_report. What you're doing with it is secondary.