data-pipelines

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Translated

Use this skill for data pipeline work — ingestion with dlt, transformations with sqlmesh, analytics with DuckDB/MotherDuck, DataFrames with polars, notebooks with marimo, and project management with uv.

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npx skill4agent add kylelundstedt/dotfiles data-pipelines

Tags

Translated version includes tags in frontmatter
data-pipelinedlt-ingestionsqlmesh-transformationduckdb-analyticsuv-project-management

SKILL.md Content

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You are building data pipelines using a DuckDB-centric stack. The tools, in typical execution order: dlt (extract + load) → sqlmesh (transform) → DuckDB/MotherDuck (query engine) → polars (DataFrame work) → marimo (notebooks/apps). uv manages Python projects and dependencies.

Language Preference

SQL first (DuckDB dialect), then Python, then bash. Use the simplest language that gets the job done.

uv — Project Management

Never use pip directly. All Python work goes through uv.
bash
uv init my-project                    # New project
uv add "dlt[duckdb]" sqlmesh polars   # Add dependencies
uv sync                               # Install into .venv
uv run python pipeline.py             # Run in project venv
uv run --with requests script.py      # Ad-hoc dependency
Inline script dependencies (PEP 723) for standalone scripts:
python
# /// script
# dependencies = ["dlt[duckdb]", "polars"]
# requires-python = ">=3.12"
# ///
Run with 
uv run script.py
— deps are resolved automatically.
Always commit 
uv.lock
. Use 
pyproject.toml
for dependency declarations, never 
requirements.txt
.

dlt — Extract + Load

dlt handles ingestion: API calls, pagination, schema inference, incremental loading, and state management.

Scaffold and Run

bash
dlt init rest_api duckdb             # Scaffold pipeline
uv run python pipeline.py           # Run extraction
dlt pipeline <name> info             # Inspect state
dlt pipeline <name> schema           # View inferred schema

Pipeline Patterns

Minimal pipeline:
python
import dlt

pipeline = dlt.pipeline(
    pipeline_name="my_pipeline",
    destination="duckdb",
    dataset_name="raw",
)
info = pipeline.run(data, table_name="events")
Incremental loading:
python
@dlt.resource(write_disposition="merge", primary_key="id")
def users(updated_at=dlt.sources.incremental("updated_at")):
    yield from fetch_users(since=updated_at.last_value)
REST API source (declarative):
python
from dlt.sources.rest_api import rest_api_source

source = rest_api_source({
    "client": {"base_url": "https://api.example.com/v1"},
    "resource_defaults": {"primary_key": "id", "write_disposition": "merge"},
    "resources": [
        "users",
        {
            "name": "events",
            "write_disposition": "append",
            "endpoint": {
                "path": "events",
                "incremental": {"cursor_path": "created_at", "initial_value": "2024-01-01"},
            },
        },
    ],
})
Write dispositions:
DispositionBehaviorUse For
append
Insert rows (default)Immutable events, logs
replace
Drop and recreateSmall lookup tables
merge
Upsert by 
primary_key
Mutable records
Destinations: 
duckdb
(local file), 
motherduck
(cloud). Set 
motherduck_token
env var or configure in 
.dlt/secrets.toml
.

Project Structure

.dlt/
  config.toml          # Pipeline config
  secrets.toml         # Credentials (gitignored)
<source>_pipeline.py

sqlmesh — Transform

SQL-first transformation framework. Models are SQL files with a header block. Plan/apply workflow — no accidental production changes.

Scaffold and Run

bash
sqlmesh init duckdb                              # New project
sqlmesh init -t dlt --dlt-pipeline <name>        # From dlt schema
sqlmesh plan                                     # Preview + apply (dev)
sqlmesh plan prod                                # Promote to production
sqlmesh fetchdf "SELECT * FROM analytics.users"  # Ad-hoc query
sqlmesh test                                     # Run unit tests
sqlmesh ui                                       # Web interface

Model Kinds

KindBehaviorUse For
FULL
Rewrite entire tableSmall dimension tables
INCREMENTAL_BY_TIME_RANGE
Process new time intervalsFacts, events, logs
INCREMENTAL_BY_UNIQUE_KEY
Upsert by keyMutable dimensions
SEED
Static CSV dataReference/lookup data
VIEW
SQL viewSimple pass-throughs
SCD_TYPE_2
Slowly changing dimensionsHistorical tracking

Model Example

sql
MODEL (
    name analytics.stg_events,
    kind INCREMENTAL_BY_TIME_RANGE (time_column event_date),
    cron '@daily',
    grain (event_id),
    audits (NOT_NULL(columns=[event_id]))
);

SELECT
    event_id,
    user_id,
    event_type,
    event_date
FROM raw.events
WHERE event_date BETWEEN @start_date AND @end_date

Config (
config.yaml
)

yaml
gateways:
  local:
    connection:
      type: duckdb
      database: db.duckdb
default_gateway: local
model_defaults:
  dialect: duckdb

dlt Integration

sqlmesh init -t dlt
auto-generates external models and incremental staging models from dlt's inferred schema. Schema changes from dlt are detected by 
sqlmesh plan
.

DuckDB — Query Engine

DuckDB is the shared SQL engine across the entire stack. Use DuckDB-specific syntax freely.

CLI

bash
duckdb                              # In-memory
duckdb my_data.db                   # Persistent local
duckdb md:my_db                     # MotherDuck
duckdb -c "SELECT 42"              # One-shot

DuckDB SQL Syntax

Friendly SQL:
sql
FROM my_table;                                          -- Implicit SELECT *
FROM my_table SELECT col1, col2 WHERE col3 > 5;        -- FROM-first
SELECT * EXCLUDE (internal_id) FROM events;             -- Drop columns
SELECT * REPLACE (amount / 100.0 AS amount) FROM txns;  -- Transform in-place
SELECT category, SUM(amount) FROM sales GROUP BY ALL;    -- Infer GROUP BY
Read files directly (no import step):
sql
SELECT * FROM 'data.parquet';
SELECT * FROM read_csv('data.csv', header=true);
SELECT * FROM 's3://bucket/path/*.parquet';
COPY (SELECT * FROM events) TO 'output.parquet' (FORMAT PARQUET);
Nested types:
sql
SELECT {'name': 'Alice', 'age': 30} AS person;
SELECT [1, 2, 3] AS nums;
SELECT list_filter([1, 2, 3, 4], x -> x > 2);
Useful commands:
sql
DESCRIBE SELECT * FROM events;
SUMMARIZE events;

MotherDuck

sql
ATTACH 'md:';              -- All databases
ATTACH 'md:my_db';         -- Specific database
Auth via 
motherduck_token
env var. Cross-database queries work: 
SELECT * FROM local_db.main.t1 JOIN md:cloud_db.main.t2 USING (id)
.

polars — DataFrames

Use polars when Python logic is needed — complex string transforms, ML features, row-level conditionals. For joins, aggregations, and window functions, prefer SQL.

Key Patterns

python
import polars as pl

# Lazy evaluation (always prefer for production)
lf = pl.scan_parquet("events/*.parquet")
result = (
    lf.filter(pl.col("event_date") >= "2024-01-01")
    .group_by("user_id")
    .agg(pl.col("amount").sum().alias("total_spend"))
    .sort("total_spend", descending=True)
    .collect()
)

# Three contexts
df.select(...)         # Pick/transform columns (output has ONLY these)
df.with_columns(...)   # Add/overwrite columns (keeps all originals)
df.filter(...)         # Keep rows matching condition
DuckDB interop (zero-copy via Arrow):
python
import duckdb
result = duckdb.sql("SELECT * FROM df WHERE amount > 100").pl()

marimo — Notebooks

Reactive Python notebooks stored as plain 
.py
files. Cells auto-re-execute when dependencies change.
bash
marimo edit notebook.py              # Create/edit
marimo run notebook.py               # Serve as app
marimo convert notebook.ipynb -o out.py  # From Jupyter
SQL cells use DuckDB by default and return polars DataFrames:
python
result = mo.sql(f"""
    SELECT * FROM events
    WHERE event_date >= '{start_date}'
""")
Python variables and polars DataFrames are queryable from SQL cells and vice versa.

Typical Pipeline Flow

  1. uv init
    + 
    uv add "dlt[duckdb]" "sqlmesh[duckdb]" polars marimo
  2. dlt init rest_api duckdb
    — scaffold extraction
  3. uv run python pipeline.py
    — dlt loads raw data into DuckDB
  4. sqlmesh init -t dlt --dlt-pipeline <name>
    — generate transform models
  5. Write SQL models → 
    sqlmesh plan
    — transform raw into analytics
  6. marimo edit analysis.py
    — explore with SQL cells and polars
  7. For production: swap destination to 
    motherduck
    , 
    sqlmesh plan prod