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.

Skill check: Data Cleaning and Transformation

Eight timed questions drawn from a bank covering CASE, COALESCE and NULLIF, casting, string and pattern functions, dates and durations, standardization, deduplication and validation queries, on the shop, clinic, freight and people datasets. Each answer is graded on the public data and on a hidden variant, so write the rule, not the answer.

Questions
8 drawn from 17
Time
35 minutes
Pass mark
75%
Retake
after 6 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.
  • The timer is kept on the server and covers writing your answers. When time runs out, your saved answers are graded as they are.
  • 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

  • CASE expressions
  • COALESCE and NULLIF
  • CAST and type conversion
  • String functions
  • Date and time functions
  • Detecting and removing duplicates
  • Standardizing inconsistent values
  • Validation and data-quality queries
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.