# Add data to a Parquet export safely

A Parquet export is a complete file with a schema and footer. Appending the bytes from another `SELECT ... FORMAT parquet` does not produce a single combined file. Treat each export as an independent artifact or create a new file containing the intended combined rows.

## Rebuild a combined export

Load the existing file into a table with an explicit compatible schema. Insert the additional rows, validate the result, then export a new file using the native client's exact-byte output:

```sh
./coordinator client --database data \
  --query 'SELECT id, name FROM people ORDER BY id FORMAT parquet' \
  > people-new.parquet
```

Only replace the previous artifact after the command succeeds and the new file passes a read-back check. A shell redirect can create a partial file before a query reports an error; an existing filename is therefore not proof of success.

## Keep files separate when appropriate

For periodic exports, choose a unique filename per batch and maintain a manifest outside SQL. Consumers can process those files as separate datasets. Coordinator DB's server `file()` source reads one confined regular file; it does not expand path patterns or append files.

See [Parquet format](https://coordinatordb.com/docs/reference/formats/parquet/parquet), [native client output](https://coordinatordb.com/docs/concepts/features/interfaces/client) and [file source](https://coordinatordb.com/docs/reference/functions/table-functions/file).