SQL Practice
SQL Interview Questions & Practice Guide
The SQL topics that come up most in interviews are window functions (running totals, rankings, moving averages), aggregations with GROUP BY, joins (including anti-joins and self-joins), and NULL handling — NULL comparison semantics trip up more candidates than any join syntax does. Ediky's SQL bank weights window functions heaviest for exactly that reason: they're the topic candidates most often haven't practiced enough.
SQL topics by real weight in Ediky's bank
- Window Functions (7) — running totals, rankings with ties, moving averages
- Aggregations (4) — GROUP BY, HAVING, and the classic "top N per group" problem
- Set Operations (3) — UNION/INTERSECT/EXCEPT and reconciling two datasets without a full outer join
- NULL Handling (2) — why AVG and SUM/COUNT disagree, and anti-joins that silently return nothing
- Joins, CTEs, Subqueries, Pivoting, Indexing & Performance, Date & Time — 1-2 questions each
Real questions from Ediky's SQL bank
Actual question titles, by topic:
- "Nth Highest Spending Customer (With Ties)" (Window Functions)
- "Running Balance After Each Transaction" (Window Functions)
- "Why AVG Disagrees with SUM Over COUNT" (NULL Handling)
- "The Anti-Join That Silently Returned Nothing" (NULL Handling)
- "Reconcile Two Price Feeds With No FULL OUTER JOIN" (Set Operations)
Why the questions aren't textbook syntax drills
Ediky's SQL questions are framed as real scenarios (a teammate's confusing result, a query that returns nothing when it shouldn't) rather than "write a query to do X" — closer to how SQL interview questions actually get asked, and closer to on-the-job debugging than syntax memorization.
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