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Refresh your SQL

Is your SQL a bit rusty? Brush it up in a few evenings.

Maybe you learnt SQL at school, at college or in a previous job, and it's been a while. The words vaguely come back, but writing a LEFT JOIN or a HAVING without looking it up is another story.

With Lurndo you quickly work through what you still know, run into the pitfalls you'd forgotten, and pick up what has become standard since.

Start free with the first lessonNo account needed · a lesson takes a few minutes

Why Lurndo suits you

  • Quickly through what you know

    Lessons take a few minutes, so you breeze through the basics again. You can also read up on any topic straight away on the topic pages.

  • The pitfalls you'd forgotten

    = NULL that never finds anything, AND that goes before OR, 7 / 2 that gives 3. The exercises show you exactly where it goes wrong.

  • Further than before

    Window functions such as ROW_NUMBER and RANK, and CTEs with WITH, are now in almost every database. The last modules explain them.

  • Everything on one page

    The SQL cheat sheet sums up the whole course, with a working example for every part.

Do you remember?

Show every team with the name of its coach, including the teams that don't have a coach (yet).

Where it usually rusts

Counting and grouping, combining tables, subqueries and window functions. Start with what you're least sure of.

  1. 4Fourth dayYour fourth client: De Trapper bike rental in Bruges. You learn to count, add up and average with COUNT, SUM, AVG, MIN and MAX, and to summarise everything per group with GROUP BY and HAVING.
  2. 5Fifth dayYour fifth client: football club FC De Kraaien in Lier. You learn to combine tables with keys and JOIN: INNER, LEFT, RIGHT and FULL, with aliases, across several tables and even a table with itself.
  3. 6Sixth dayYour sixth client: Het Leeslint library in Kortrijk. You learn to query smarter: reshaping text and dates, choosing with CASE, asking questions inside questions with subqueries and EXISTS, and keeping long queries readable with WITH.
  4. 8Eighth dayYour eighth client: the Ronde van het Pajottenland, a five-day stage race. You learn window functions: numbering with ROW_NUMBER, ranking with RANK, per group with PARTITION BY, standings with running totals, and combining lists with UNION.

Frequently asked questions

Can I skip lessons?

Lessons open one after another, so you don't miss anything, but they only take a few minutes. If you want to read something up straight away, every topic is also open on the topic pages.

What's new since I was at college?

Mainly window functions and CTEs. They make ranking, running totals and complicated queries much simpler, and almost every modern database supports them.

Is there an overview to revise quickly?

Yes, the SQL cheat sheet puts everything from the course on one page, to keep or print.

A quick refresher?

Start the first lesson and see how quickly it comes back. The first three modules are free.

Start free with the first lesson
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