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my @avgs  = $dbh->selectrow_array($avgSQL);

...
# CSV output method B (2-columns)
print "Col,Avg\n";
printf("%s,%f\n", $cols[$_], $avgs[$_]) for 0 .. $#cols;

my %avgsHash;
@avgsHash{ @cols } = @avgs;  # uses a hash slice to populate %avgsHash
print "Col,Avg\n";
printf("%s,%f\n", $_, $avgsHash{$_}) for @cols;