windmill/system_prompts/languages/duckdb.md

DuckDB

Arguments are defined with comments and used with $name syntax:

-- $name (text) = default
-- $age (integer)
SELECT * FROM users WHERE name = $name AND age > $age;

Ducklake Integration

Attach Ducklake for data lake operations:

-- Main ducklake
ATTACH 'ducklake' AS dl;

-- Named ducklake
ATTACH 'ducklake://my_lake' AS dl;

-- Then query
SELECT * FROM dl.schema.table;

External Database Connections

Connect to external databases using resources:

ATTACH '$res:path/to/resource' AS db (TYPE postgres);
SELECT * FROM db.schema.table;

S3 File Operations

Read files from S3 storage:

-- Default storage
SELECT * FROM read_csv('s3:///path/to/file.csv');

-- Named storage
SELECT * FROM read_csv('s3://storage_name/path/to/file.csv');

-- Parquet files
SELECT * FROM read_parquet('s3:///path/to/file.parquet');

-- JSON files
SELECT * FROM read_json('s3:///path/to/file.json');

Receiving an S3Object as a script parameter

Declare the arg with type (s3object). Windmill renders an S3 file picker for it and binds the arg as the bare s3://storage/key URI, which DuckDB's reader functions consume directly:

-- $file (s3object)
SELECT * FROM read_parquet($file);

Works with any DuckDB reader: read_csv($file), read_json($file), etc.

Writing query results to S3

DuckDB writes to S3 natively via COPY ... TO:

COPY (SELECT * FROM users) TO 's3:///exports/users.parquet' (FORMAT PARQUET);

Use this instead of the -- s3 streaming directive supported by the other SQL dialects — that directive is not available in DuckDB.