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Databases and SQL

The relational model, ERDs, keys and normalisation, then SQL queries that join tables and aggregate. You run the queries right in the browser.

1 lesson5 tasks135 points in totalTask difficulty: 1 easy, 4 medium

Company data does not live in spreadsheet files but in databases. Here you learn to design them without duplicates and to ask them questions in SQL.

Lessons

Read first, then practise on the tasks.

  1. Lesson 1

    From ERD to tables: design without duplicates

    Turn entities, relationships and keys into tables that never contradict themselves. Normalisation without fear of the jargon.

    ~12 minup to 50 pts

Tasks

  1. Reading an ERD and the M:N relationship

    choice10 pts
    ERDcardinalityjunction table

  2. Which normal form is broken?

    choice15 pts
    normalisation2NF3NFanomalies

  3. How many rows does a LEFT JOIN return?

    number15 pts
    SQLJOINLEFT JOIN

  4. Customer spend in SQL

    code25 pts
    SQLJOINGROUP BYHAVINGsqlite

  5. Design the tables for a library

    text20 pts
    database designERDkeysnormalisation