Fix issue where pandas<1.4.0 doesn't return the number of rows

src/datasets/io/sql.py

@@ -114,7 +114,7 @@ def _write(self, conn: Connection, **to_sql_kwargs) -> int:
                 df = self._batch_sql(offset)
                 written += df.to_sql(
                     self.table_name, conn, **to_sql_kwargs, if_exists="replace" if offset == 0 else "append"
-                )
+                ) or len(df)
 
         else:
             num_rows, batch_size = len(self.dataset), self.batch_size