Most practice tests what you remember.D8LooP tests what you’d decide.

Nobody gets hired for reciting a definition. Turn any one of these over.

• you can revise thisSlowly changing dimension, type 2A new row per change, with valid-from and valid-to dates.turn it overnobody revises for thisThe customer moved house. Which address goes on last month’s invoice — and who finds out if you pick wrong?back
• you can revise thisIdempotencyRunning it twice leaves the same result as running it once.turn it overnobody revises for thisThe file landed twice at 03:00. Which numbers already went out, and what do you tell the person holding them?back
• you can revise thisGrainWhat exactly one row of the table represents.turn it overnobody revises for thisRefunds arrive a week late and partial. Does a row still mean an order, or does that quietly break the total?back

Three beats, every scenario — and each one runs on its own here.

• 01

  Interviewing soon

  You can write the query. You have never been asked to justify the schema under it.

• 02

  Two years in

  Everything you have built started from a table someone else designed.

• 03

  Senior, out of practice

  You make these calls weekly. Saying why, in nine minutes, is the rusty part.

• 04

  Starting from scratch

  New to data engineering. One roadmap takes you from Python and SQL to pipelines and Spark, a decision at a time.

  See the roadmap →

One person builds this, in evenings. So this is what is moving, what is stopped, and why — rather than a roadmap that only lists the good news.

1. In progress

   Data engineering projects

   End-to-end briefs instead of single scenarios: ingest it, model it, load it, test it, and write up the decisions. The thing you can actually point at in an interview.

2. Ongoing

   Deeper scenarios

   Pipelines, Modeling, SQL and Python, reworked one scenario at a time up to the depth the newest ones already have. One person, most evenings — which is why it is a standing item and not a date.

3. Open

   Collaborators

   If you have sat on either side of these interviews and would rather build something than complain about them, I would like to hear from you. This should stop being a one-person project.