# File schemas

An input format describes bytes; the target schema determines how those bytes become typed SQL values. Create an explicit destination table for INSERT FORMAT.

Most server `file()` sources also require a third argument containing a column/type list, including CSV, JSON, Arrow, Parquet and Avro. A container's stored schema does not replace this requirement in CoordinatorDB.

## Sources with column metadata

Two formats can provide file-source columns without the schema argument:

* `form` infers String columns from its field names. Empty input needs an explicit schema.
* `parquet_metadata` exposes a fixed schema describing the file footer.

Form keys are literal field names; its values are URL-decoded. An explicit supplied schema follows ordinary conversions and cannot contain column constraints or DEFAULT expressions.

## Examples

```text
SELECT * FROM file('people.csv', csv, 'id UInt64, name String');
SELECT * FROM file('fields.form', form);
SELECT num_rows FROM file('sample.parquet', parquet_metadata);
```

The files must exist under the configured server file root. See [`file`](https://coordinatordb.com/docs/reference/functions/table-functions/file), [form](https://coordinatordb.com/docs/reference/formats/form) and [Parquet metadata](https://coordinatordb.com/docs/reference/formats/parquet/parquet-metadata).