message: [skip ci] add comment for oracle schema fetching
diff: @@ -106,6 +106,9 @@ where
  let conn = self.pool.get()?;
  for (i, query) in self.queries.iter().enumerate() {
  // assuming all the partition queries yield same schema
  + // without rownum = 1, derived type might be wrong
  + // example: select avg(test_int), test_char from test_table group by test_char
  + // -> (NumInt, Char) instead of (NumtFloat, Char)
  match conn.query(limit1_query_oracle(query)?.as_str(), &[]) {
  Ok(rows) => {
  let (names, types) = rows
  