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SQL Articles & Tutorials
Expert-written tutorials, guides, and deep dives into SQL — from basics to advanced optimization. Direct answers, examples, and FAQs.
learn & grow
SQL Articles & Tutorials
Expert-written tutorials, guides, and deep dives into SQL — from basics to advanced optimization. Direct answers, examples, and FAQs.
Read Latest Practice SQL- Guides + deep dives
- Interview-ready tips
- Free to read
// LATEST ARTICLES41 ARTICLES
Best Practices★ Featured
Idempotent SQL: Writing Safe, Re-runnable Scripts
Learn to write idempotent SQL for migrations, seed scripts, and ETL jobs — safe upserts, guarded schema changes, and the relative-update trap that compounds on re-run.
SqlInt team6 min read
Window Functions & CTEs6 min read
Running Totals and Moving Averages in SQL
Learn to calculate running totals, moving averages, and percent-of-total in SQL using window functions and frame clauses, with common mistakes and date-gap handling.
SqlInt team6 min read
Best Practices7 min read
SQL Injection: How It Works and How to Prevent It
Learn how SQL injection attacks actually work — authentication bypass, UNION-based data exfiltration — and how parameterized queries prevent them structurally.
SqlInt team7 min read
Window Functions & CTEs7 min read
SQL Window Functions: The Complete Guide
A complete guide to SQL window functions — RANK, DENSE_RANK, ROW_NUMBER, LAG/LEAD, NTILE, and aggregate window functions, with frame clauses and performance notes explained.
SqlInt team7 min read
Interview Prep11 min read
Top 20 SQL Interview Questions and Answers for 2026
Prepare for your SQL interview with all 20 essential questions covering joins, window functions, CTEs, indexing, transactions, and optimization, plus 5 bonus practical query challenges.
SqlInt team11 min read
Query Patterns7 min read
The Gaps and Islands Problem in SQL: A Complete Guide
Master the gaps and islands SQL interview pattern — find consecutive streaks and missing values using ROW_NUMBER, LAG, and running-sum techniques, with database compatibility notes.
SqlInt team7 min read
Product Analytics6 min read
Product Analytics SQL: Funnels, Retention, and Cohorts
Learn the three core product analytics SQL patterns — funnel analysis, retention (Day-1/7/30), and cohort analysis — using a standard events table, with common mistakes explained.
SqlInt team6 min read
Fundamentals6 min read
String Functions in SQL: A Practical Guide
A practical guide to SQL string functions — CONCAT, SUBSTRING, TRIM, REPLACE, and REGEXP — with a real data-cleaning example and the CONCAT vs || NULL-handling difference.
SqlInt team6 min read
Fundamentals5 min read
GROUP BY vs HAVING vs WHERE: The Complete Guide
Understand exactly how WHERE, GROUP BY, and HAVING execute in SQL, with the real logical execution order, common mistakes, and why filtering early with WHERE is faster.
SqlInt team5 min read
Fundamentals10 min read
SQL JOINs Explained: INNER, LEFT, RIGHT, FULL, and CROSS
A complete guide to SQL JOINs with practical examples, performance notes, and common mistakes. Covers INNER, LEFT, RIGHT, FULL OUTER, CROSS, self joins, and semi/anti-joins.
SqlInt team10 min read
FAQ
SQL Articles — FAQ
What SQL topics do the articles cover?
Interview prep, query patterns, window functions and CTEs, performance and optimization, fundamentals, and best practices — from beginner SELECT queries to advanced grouping, joins, and subqueries.
Are the SQL articles free?
Yes. All published articles on SqlInt are free to read with no signup required, and most include a free PDF download.
Can I download articles as PDF?
Yes. Every article page has a Download PDF button that generates a printable PDF with working links — including the free SQL cheat sheet.
How often are new articles published?
New tutorials and guides are added regularly. Subscribe via the RSS feed at sqlint.com/rss.xml to get new articles as they publish.
Where should beginners start?
Start with the Beginner and Fundamentals categories, then move to Interview Prep and Query Pattern articles once you can write basic SELECT, WHERE, GROUP BY, and JOIN queries.