You could look for all filenames that match the current filename maybe?

select
filename
from $database_table
where filename like '$filename%.html'
order by filename desc
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If your database allows you regular expressions, you can even match the filename plus digits at the end.

Also, let me recommend that you rewrite your Do_SQL routine as a routine that takes the SQL as a parameter?

A first implementation could be:

sub Do_SQL2 {
    my( $sql ) = @_;
    $sth = $dbh->prepare( $sql );
    $sth->execute();
}
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Then you can call it in a saner way without using global variables:

Do_SQL2($SQL);
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