Challenge Hub
This hub collects the standalone SQL challenge pages that have already been expanded into durable learning assets. Use them when you want a focused practice rep with solution approaches, pitfalls, and related guides.
Indexable
19
Challenge pages currently eligible for sitemap inclusion and search indexing.
In Expansion
0
Candidate challenge pages still being expanded before they become indexable.
Use This Hub
When you want a deeper challenge detail page than `/daily`, but a lighter unit of practice than a full interview prompt.
These challenge pages already have a minimum content standard: explanation, schema summary, solution approaches, pitfalls, and related guides.
Find products that never appear in the order table without being fooled by missing or duplicate order rows.
Find the second distinct highest salary without accidentally returning the same maximum twice.
Find values that appear in at least three consecutive rows instead of merely appearing three times anywhere in the table.
Compare each weather row with the previous day and return only the IDs where temperature increased day over day.
Match patients whose condition list contains a Type I diabetes code without being fooled by partial code overlaps.
Assign tied scores the same rank while keeping the next rank consecutive with no gaps.
Swap every pair of adjacent seat IDs while leaving the final row untouched if the seat count is odd.
Compute daily cancellation rate after excluding any trip where either the client or driver is banned.
Calculate contest participation rate by dividing each contest’s registrations by the total user base, not by contest-local counts.
Roll monthly transaction reporting into one query while splitting total volume from approved volume by country.
Measure what share of customers got an immediate delivery on their first-ever order instead of across all orders.
Compute next-day retention by checking whether each player returned on the day after their first login.
Sum 2016 investment value only for policyholders who meet one duplicate condition and one uniqueness condition at the same time.
Use a running total to find the last passenger whose cumulative weight still stays under the bus limit.
Reconstruct each product’s price as of a snapshot date, including products that had not changed yet and still use the default price.
Calculate per-stock capital gain or loss by treating buys as cash outflows and sells as cash inflows before summing them.
Calculate overall friend request acceptance rate while separating request volume from accepted pairs cleanly.
Classify each tree node as root, inner, or leaf based on whether it has a parent and whether it is referenced by children.
Return only the customers whose distinct purchased product set covers every product listed in the catalog.
This page is designed as the evergreen practice library for SQL Boy. The daily page is still the rotating entry point when you want a single practice rep chosen by date, but the challenge hub serves a different job: it helps readers discover durable, topic-driven SQL problems that deserve to rank on their own and stay useful over time. If someone searches for a specific SQL interview question, a classic anti-join problem, a ranking exercise, or a point-in-time reporting pattern, the standalone challenge page is the destination that should satisfy that intent.
Each challenge detail page is built to do more than show a prompt and a final answer. The goal is to preserve the original hands-on practice experience while also adding the explanation layer that many challenge sites leave too thin. That is why the indexable pages include a schema summary, multiple solution approaches when the pattern matters, common mistakes, related blog guides, and internal links to nearby challenge reps. In practical terms, this means you can use the hub in several ways: as a self-study library, as an interview drill catalog, or as a concept map when you know the SQL pattern you need to practice but do not want to dig through random archives.
The simplest way to use this page is to choose a challenge that matches the skill you want to sharpen, solve it in the editor, and then read the explanation only after you have committed to a query shape of your own. If you are weak on time-series logic, window functions, conditional aggregation, or subquery design, use the challenge detail page as the narrow drill and the related guide links as the deeper follow-up reading. That workflow is deliberate. The hub is supposed to help you move from isolated SQL reps into repeatable understanding instead of collecting disconnected solutions that are hard to reuse later.
The current challenge set is intentionally weighted toward the SQL patterns that matter most in interviews and real reporting work. Instead of publishing hundreds of thin pages with no explanation, the library prioritizes problems that teach durable mental models: anti-joins, relational division, running totals, dense ranking, conditional aggregation, row-sequence analysis, first-event cohorts, next-day retention, and point-in-time state reconstruction. These are the kinds of queries that appear repeatedly in analytics teams, product dashboards, finance reporting, and technical interviews because they force you to get row grain, filtering order, and business definition correct at the same time.
Difficulty Mix
Easy: 1 challenges. Medium: 16 challenges. Hard: 2 challenges.
Most Common Concepts
That mix matters for SEO and for user value. A challenge hub should not just look large; it should cover the search intents that serious learners actually have. Some people arrive by exact problem name, others by pattern searches like “SQL cancellation rate” or “second highest salary SQL”, and others by concept gaps such as window functions, date logic, or ranking semantics. The standalone challenge format allows one page to answer the immediate query while the rest of the internal links lead the user into a broader learning path. That is why this library now sits between the rotating `/daily` workflow and the larger blog/tutorial system. It is the bridge between practice and explanation.
If you are using this hub strategically, start by choosing one repeated weakness and working through several related challenge pages back to back instead of hopping randomly. For example, if ranking queries are the weak point, practice the ranking pages and then follow the related window-function guides. If denominator choice and rate calculations are the problem, use the conversion, cancellation, and participation challenges as a mini cluster. The library is more useful when treated as a set of learning paths, not just a flat list of prompts.