Principal Data Engineer — Live Interview Repo

You've inherited this repo from a contractor. Finance is asking questions about the numbers it produces. Your job: investigate, fix, and improve.

Setup (do this BEFORE the interview)

Required: Python 3.11 or 3.12 (dbt doesn't yet support 3.13+; uv will auto-fetch 3.12 via .python-version if you don't have it), uv (https://docs.astral.sh/uv/getting-started/installation/), make, git.

uv sync
make setup

make setup builds the DuckDB warehouse from the committed seed CSVs and runs dbt once. The seed CSVs and DATA-123.md are committed to the repo — you don't need to regenerate them. Re-running make setup rebuilds the warehouse and re-renders DATA-123.md from the template, so don't edit that file directly if you want notes to persist.

Daily commands

make run      # dbt run (incremental)
make full     # dbt run --full-refresh
make test     # dbt test
make lint     # sqlfluff lint
make sql Q="select count(*) from main_orders_dw.order_fact"   # single-shot read-only query
make clean    # remove warehouse.duckdb (rebuild with `make setup`)

For an interactive REPL against the warehouse, install the DuckDB CLI separately (e.g. brew install duckdb) and open it read-only:

duckdb -readonly warehouse.duckdb

Where things live

• DATA-123.md — your ticket. Read this first.
• models/ — dbt models (orders, merchants).
• setup/ — seed generator + SQL runner.
• tests/ — singular dbt tests.
• docs/designs/ — prior design docs from the team.
• CONTRIBUTING.md — team conventions.

Bring your own AI tool

Claude Code, Cursor, Codex, etc. — bring whatever you're fast in.

Submitting your work

This repo is owned by the Extend org, so you can't push branches directly to it. Instead, submit via a fork:

1. Fork this repo to your own GitHub account (the "Fork" button, top-right on GitHub). With the gh CLI: gh repo fork helloextend/poc-data-engineering-coding-challenge --clone.
2. Do your work on a branch in your fork.
3. Push your branch to your fork.
4. Open a Pull Request targeting helloextend/poc-data-engineering-coding-challenge:master. With the gh CLI: gh pr create --repo helloextend/poc-data-engineering-coding-challenge --base master --head <your-github-username>:<your-branch>.

The PR will appear in this repo's Pull Requests tab. An Extend team member will review it there.