SQL Quest

Lessons, hints, explained solutions, the in-browser PostgreSQL editor and practice answer checks in your browser are available. Graded assessments, recorded progress from answer checks and new certificates aren't available yet.

SQL placement diagnostic

Fourteen short, untimed questions that start with a single SELECT and finish with window functions and data cleaning. You get two questions from each of the first seven tracks (foundations, retrieving and filtering, aggregation, joins, subqueries, analytics, cleaning), easiest first. Your results show which skills you already have and recommend the track to start with. It never marks lessons as complete, so skip a question rather than guess: an honest result gives the best recommendation.

Questions
14 drawn from 28
Time
Untimed
Pass mark
No pass/fail
Retake
after 24 hours

How it works

  • Questions are drawn at random across the skills below, easiest first. A retake avoids the questions of your previous attempt wherever the question bank has others for that skill.
  • You can run queries on the real dataset as often as you like. Answers save as you type; nothing is graded until you submit.
  • A query that errors or runs longer than the grader's time limit counts as not correct. A problem on our side (for example the grader being busy) never does: the attempt stays open with your answers saved, and you can submit again.
  • Each answer is graded by results on the dataset and on a hidden copy with different rows. Afterwards you see which answers passed, with the model solution and an explanation.
  • It's open-book and not proctored.

Skills covered

  • SELECT and FROM
  • Primary and foreign keys
  • NULL and three-valued logic
  • LIMIT, OFFSET and top-N
  • GROUP BY
  • HAVING
  • INNER JOIN
  • LEFT JOIN and missing matches
  • Scalar subqueries
  • EXISTS and NOT EXISTS
  • ROW_NUMBER, RANK, DENSE_RANK
  • Running totals
  • CASE expressions
  • COALESCE and NULLIF
Not available yet. Graded assessments aren't available yet: they need SQL Quest's server-side grader, which is switched off until its security review is complete. You can still practise every lesson and check practice answers in your browser.