Find out what you really know
Reading a lesson feels like learning. Answering without it open is how you find out. Incidents to work through, quizzes that explain every answer, and mock interviews for data roles, with your progress kept in this browser. No account.
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Subject
What is the purpose of Python lists?
Not this time. Python lists are used to store multiple items in a single variable.
Scenarios
An incident with AI, an agent or a data system, the evidence, and the calls to make. Then what really went wrong.
- How AI works · beginnerThe AI test that passes on Monday and fails on TuesdayA test of an AI feature fails about 1 run in 6, and since a model upgrade it fails most runs. Nothing in the code changed. Find out why, and write a test that means something.
- Data engineering in the AI era · beginnerThe revenue dashboard that is 17% too highApril revenue on the sales dashboard is 17.2% above finance's figure, and the board meeting is at 14:00. Find the cause in the query, not in the warehouse.
- How AI works · beginnerThe warranty the help bot inventedA customer was promised a 2-year warranty on a refurbished laptop. There is no such warranty. Work out why the bot said it, and what stops the next one.
- AI agents · intermediateThe agent bill that grew 5 times in a monthA coding agent's monthly bill went from $1,200 to $6,700 while the number of tasks rose by a fifth. Find where the money went before you cut the wrong thing.
Quizzes
- PythonBeginnerStart Every Python quiz
- SQLBeginnerStart Every SQL quiz
- PySparkExpert · Beginner · IntermediateStart Every PySpark quiz
- DatabricksBeginner · IntermediateStart Every Databricks quiz
- GenAIBeginner · IntermediateStart Every GenAI quiz
- AWSBeginnerStart Every AWS quiz
- AI engineeringIntermediateStart Every AI engineering quiz
- Data engineeringIntermediateStart Every Data engineering quiz
Mock interviews
From agents, RAG and evaluation to Spark, SQL and the cloud: pick your role, then the technology.
Data Engineer
- Databricks
- How does Delta Lake ensure ACID compliance on Databricks?
- Explain the difference between Apache Spark and Databricks
- AWS
- What are the core components of the AWS data lake architecture?
- What is the difference between batch processing and stream processing? Provide examples of AWS services used for each.
- Azure
- A pipeline copies data from Blob Storage to Azure SQL Database. If the source file schema changes (e.g., a new column is added), how can ADF handle this without manual intervention?
- How can you ensure data consistency when updating a Delta Lake table in Azure Data Lake Storage Gen2 using ADF, especially when dealing with concurrent updates?
- PySpark
- What are RDDs, and how are they different from DataFrames and Datasets?
- What is a Spark job, and what are stages and tasks within it?
- SQL
- Can a table have multiple primary keys?
- Can a table have multiple UNIQUE constraints?
- System design
- Design a pipeline that brings the orders, customers and products tables from the company's PostgreSQL database into a lakehouse for daily reporting, with history and room to grow.
- Design a pipeline for website and app click events, about 50,000 events per second at peak, that feeds a dashboard updated every minute and keeps all raw events for analysis.
- Kafka and streaming
- How does Kafka keep messages in order, and what breaks that order? A team wants every event for one customer processed in the order it happened, and plans to add partitions later as traffic grows.
- What do acks=all and min.insync.replicas do together? A topic has 3 copies. Which settings lose no acknowledged message when a broker dies, and what happens to producers when 2 of the 3 brokers are down?
- dbt
- Why does dbt use ref() and source() instead of table names? A new engineer has written FROM analytics.stg_orders in a model and asks why the reviewer wants {{ ref('stg_orders') }}.
- How do you choose a dbt materialization? A project builds every model as a table, the nightly run now takes 3 hours, and a dashboard on a 2-billion-row events model is the slowest part.
- Airflow
- What is the data interval in Airflow? A new daily Dag with start_date set to today did not run today, and a colleague asks how to load the last 30 days it missed.
- An Airflow task failed after loading half its rows, was retried, and the table now has duplicates. Another task loads 'yesterday' with datetime.now(), and a rerun last week loaded the wrong day. How do you make these tasks safe to rerun?
Data Analyst
- Databricks
- What is a Databricks cluster?
- Barbara needs to join data from a Delta table with data residing in a cloud storage location. How can this be efficiently accomplished within a Databricks notebook, considering data access patterns and potential performance bottlenecks?
- AWS
- What are the core components of the AWS data lake architecture?
- What is the difference between batch processing and stream processing? Provide examples of AWS services used for each.
- SQL
- Can a table have multiple primary keys?
- Can a table have multiple UNIQUE constraints?
Data Scientist
- AWS
- What are the core components of the AWS data lake architecture?
- What is the difference between batch processing and stream processing? Provide examples of AWS services used for each.
- Azure
- Azure AI services (formerly Cognitive Services). Are they only accessible via REST APIs?
- What are the primary methods for deploying machine learning models as web services in Azure?
- SQL
- Can a table have multiple primary keys?
- Can a table have multiple UNIQUE constraints?
AI Engineer
- Agents
- What is an AI agent, and how is it different from a single chatbot call?
- Walk through the agent loop: what happens between the request and the final answer?
- LLM apps and RAG
- What is RAG, and when should you use it instead of fine-tuning or putting everything in the prompt?
- How do you write a prompt for a production LLM feature?
- Evaluation and safety
- What is the difference between jailbreaking and prompt injection, and how do defences differ?
- How do you build an evaluation set for an LLM feature?
- Prompting
- In Azure OpenAI, what distinguishes fine-tuning from prompt engineering as ways to adapt a pre-trained model?
- What are some key principles for crafting effective prompts for large language models (LLMs)?
- System design
- Design an assistant that answers employees' questions from 2 million internal documents (wikis, tickets, PDFs, policies), where each employee may only see documents they already have access to.
- Twenty teams in your company now call LLM APIs directly, each with its own keys. Design a shared LLM gateway: what it does, how requests flow through it, and what you would not put in it.
Preparing for a certification?
A free sample in the style of the real exam, with its format and what it covers. The full mock exam is on Daily Bytes.