> ## Documentation Index
> Fetch the complete documentation index at: https://docs-relytone.data.cloud/llms.txt
> Use this file to discover all available pages before exploring further.

# External Tables

> Query data on S3 object storage through external tables with automatic schema inference. Support for Parquet, JSON, and CSV formats powered by DuckDB for high-performance data access.

Relyt ONE enables querying data stored on S3 object storage through external tables. The schema is automatically inferred from the data, simplifying table creation and greatly improving usability.

External tables support **Parquet**, **JSON**, and **CSV** formats. Powered by DuckDB's `read_parquet`, `read_json`, and `read_csv` functions, they deliver efficient data access. Built-in local and remote caching reduces latency and improves throughput for optimal query performance.

## Syntax

```sql theme={null}
CREATE TABLE <table_name> () USING duckdb WITH (
  duckdb_external_location = 's3://xxxxxx',
  duckdb_external_format = 'parquet',  -- csv, json
  duckdb_external_options = ''  -- optional
);
```

## Parameters

* **`duckdb_external_location`**: S3 path to your data. See [Load Data](/features/load-data) for format details.
  * Example: `s3://s3.us-west-1.amazonaws.com/bucket/path/dat.parquet accessid=xxxx secret=yyyy`

* **`duckdb_external_format`**: Data format. Options: `parquet`, `csv`, `json`

* **`duckdb_external_options`** *(optional)*: Additional parameters passed to DuckDB.
  * Example: Include filename in results with `{"filename": true}`

<Note>
  No need to define columns explicitly—Relyt ONE automatically samples the data to infer column names and types. After creation, use `\d+ <table_name>` or `SELECT * FROM <table> LIMIT 1` to inspect the schema.
</Note>

External tables work like regular PostgreSQL tables. Queries involving external tables automatically leverage the DuckDB engine, with caching ensuring high performance regardless of S3 latency or bandwidth constraints.

## Examples

### Create a Parquet External Table

```sql theme={null}
CREATE TABLE lineitem () USING duckdb WITH (
    duckdb_external_location = 's3://s3.us-west-1.amazonaws.com/my_bucket/lineitem/*.parquet
        accessid=xxxx secret=yyyy',
    duckdb_external_format = 'parquet'
);

SELECT * FROM lineitem LIMIT 1;
```

### Create a CSV External Table with Custom Column Names

```sql theme={null}
CREATE TABLE nation () USING duckdb WITH (
    duckdb_external_location = 's3://s3.us-west-1.amazonaws.com/my_bucket/csv/nation.tbl
      accessid=xxxx secret=yyyy',
    duckdb_external_format = 'csv',
    duckdb_external_options = '{"column_names": ["n_nationkey","n_name","n_regionkey","n_comment"]}'
);
```

### Create a JSON External Table

```sql theme={null}
CREATE TABLE external_json () USING duckdb WITH (
    duckdb_external_location = 's3://s3.us-west-1.amazonaws.com/my_bucket/json/a.tbl
      accessid=xxxx secret=yyyy',
    duckdb_external_format = 'json'
);
```

**Verify the schema:**

```
\d+ external_json

                                      Table "public.external_json"
 Column |       Type       | Collation | Nullable | Default | Storage  | Compression | Stats target
--------+------------------+-----------+----------+---------+----------+-------------+--------------
 a      | bigint           |           |          |         | plain    |             |
 b      | text             |           |          |         | extended |             |
 c      | double precision |           |          |         | plain    |             |
Access method: duckdb
```