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create table d_table (
  d_table_id integer unsigned auto_increment primary key,
...
  old_value text not null,
  unique index (d_table_id, field_name)
);

$dbh->do("INSERT INTO d_table table_name = ?, operation = 'insert'", $
+table_name);

my $old_data = $dbh->selectrow_hashref("select * from 
table_to_change where primary_key_id = ?", $table_row_id);
...
           $d_table_id, $f, $old_data->{$f});

}