SQL Blog

Tutorials, interview prep and tips to level up your SQL skills — all free.

Interview PrepSQL BasicsAdvanced SQL2026

SQL JOINs Explained: INNER, LEFT, RIGHT, FULL OUTER & Real Examples

The complete advanced guide to SQL JOINs: INNER, LEFT, RIGHT, FULL OUTER, SELF, and CROSS JOIN — with 20+ real-world examples, performance optimization, a JOIN vs subquery comparison, 15 interview questions, and practice exercises.

2026-05-14·24 min read

PerformanceAdvanced SQLIndexing2026

30 SQL Performance Tips Every Developer Should Know in 2026

The complete guide to SQL query optimization. Master indexing strategies, EXPLAIN plans, pagination, N+1 patterns, JOINs, partitioning, and database-specific tuning for PostgreSQL, MySQL, and SQL Server.

2026-05-13·22 min read

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GROUP BY vs HAVING: What's the Difference?

Confused by GROUP BY vs HAVING? This guide explains the difference between GROUP BY and HAVING in SQL — with a comparison table, execution order, real-world examples, common mistakes, and FAQs.

10 min read

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SQL Window Functions Explained with Practical Examples (2026 Guide)

Master SQL window functions with practical examples. Learn ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, PARTITION BY, and OVER() with real queries for data analytics and interview prep.

28 min read

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Learn SQL for Free in 2026 — Complete Beginner's Roadmap

The complete 2026 guide to learning SQL from zero to job-ready. Free resources, a 30-day plan, salary data, career paths, code examples, and a free interactive SQL playground to practice real queries.

18 min read

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SQL Subqueries Explained: Correlated, Scalar, Inline Views & Real Examples

The complete advanced guide to SQL subqueries: correlated vs non-correlated, scalar subqueries, inline views, EXISTS vs IN, subquery vs JOIN performance, 20+ real examples, 15 interview questions, and practice exercises.

22 min read

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