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: Retrieving and Filtering Data

Eight new business questions on Wadi Market and Masar Holding data, drawn from a larger bank: calculated columns, aliases, DISTINCT, comparisons, AND / OR logic, ranges and lists, patterns, NULL, sorting, paging and date filters. Answers are graded on the public data and on a hidden variant, so write queries that are right in general, not just for today's rows.

Questions
8 drawn from 17
Time
30 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

  • Expressions and calculated columns
  • Column and table aliases
  • DISTINCT
  • WHERE with comparison operators
  • AND, OR, NOT and precedence
  • BETWEEN and IN
  • LIKE, ILIKE and pattern matching
  • NULL and three-valued logic
  • ORDER BY
  • LIMIT, OFFSET and top-N
  • Filtering dates and numbers
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.