Dear monks

I am a perl beginner and i am having trouble understanding the following code snippet 

my ($name, $source);
$sth->bind_columns(\$name, \$source);
        
my %by_source;
        
push @{$by_source{$source}}, $name while $sth->fetch;
$sth->finish;
        
if(scalar keys %by_source) {
    foreach my $s(sort {$a <=> $b} keys %by_source) {
        return shift @{$by_source{$s}};
    }
}

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I understand that 2 variables are bound to 2 columns returned from a database query. I believesth->fetch is returning an array for each database row and the first column is assigned to $name and the second column is assigned to $source.But then it looks as though the hash element  $by_source{$source} contains an array ref which is being dereferenced and the value of $name is being pushed onto that array. But that makes no sense as the hash is empty?? Perhaps once i understand this bit I will be able to work out the other lines myself (but an explanation of those lines would be appreciated).

thank you kindly

In reply to help understanding code snippet by Anonymous Monk

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