More information:

I'm having the same problem with selectall_hashref...

For a properly formatted SQL statement, the following code:

my $rl = $dbh->selectall_arrayref( $sql );
print ref $rl, "\n";
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yields: ARRAY. However, the following code:

my $rl = $dbh->selectall_hashref( $sql );
print ref $rl, "\n";
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yields nothing (empty).

What up?