SQL is the unnecessary complexity you don't want in such a simple task. Besides DBD::CSV implements a very limited subset of SQL.

What you should do is just to have a single pass over your file reading a line at the time, build your hash table of statistics along the way while splitting the records, and print out the stats at the end.

my %stats;

open MYFILE, "<data.txt" or die "Can not open file: $!";
chomp(my $heading = <MYFILE>);
my @col = split /,/, $heading;
while (my $line = <MYFILE>) {
  # build a hash for the input record
  chomp($line);
  my @rec = split /,/, $line;
  my %rec;
  @rec{@col} = @rec;
  
  # collect stats
  $stats{$rec{rec_id}}{BAL} += $rec{bal};
  $stats{$rec{rec_id}}{NUM} ++;
}

# print the stats here
for my $id (keys %rec) {
  if ($rec{$id}{NUM}) {
    print "$id => ", $rec{$id}{BAL}/$rec{$id}{NUM}, "\n" 
  }
}

close MYFILE;

[download]

In reply to Re^3: Advances SQL calculations in CSV file by Roger
in thread Advances SQL calculations in CSV file by DrAxeman

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.