Learn to build Recency, Frequency, Monetary (RFM) customer segmentation in SQL using NTILE, including the recency-inversion gotcha and segment-level reporting.

SqlInt teamJul 6, 20266 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 teamJul 6, 20266 min read

Product Analytics6 min read

A/B Test Analysis with SQL

Learn to analyze A/B tests in SQL — conversion rate by variant, sample ratio mismatch checks, a two-proportion z-test, and common statistical pitfalls like peeking.

SqlInt teamJul 6, 20266 min read

Interview Questions3 min read

Year-over-Year Growth SQL Interview Walkthrough

YoY growth questions test whether a candidate reaches for LAG or a clunky self-join, and whether they remember to guard against divide-by-zero. A full walkthrough with both engines.

SqlInt teamSep 8, 20263 min read

Database Internals7 min read

Normalization vs Denormalization in SQL: A Deep Dive

A deep dive into 1NF/2NF/3NF with real update/insert/delete anomalies, plus when and how to denormalize using duplicated columns, materialized views, and star schemas.

SqlInt teamJul 5, 20267 min read

Query Patterns7 min read

Nth Highest Salary in SQL: Every Method Explained

The definitive guide to finding the Nth highest salary in SQL — OFFSET/LIMIT, correlated subqueries, and DENSE_RANK, with correct tie-handling and top-N-per-group variants.

SqlInt teamJul 2, 20267 min read

Fundamentals5 min read

SQL Data Types Cheat Sheet: PostgreSQL, MySQL, SQL Server

A practical SQL data types reference covering numeric, string, date/time, boolean, and JSON types across PostgreSQL, MySQL, and SQL Server, with a type-selection checklist.

SqlInt teamJul 4, 20265 min read

Database Internals6 min read

SQL vs NoSQL: When to Use Which

A practical guide to choosing between SQL and NoSQL — document, key-value, column-family, and graph databases compared, plus polyglot persistence and common anti-patterns.

SqlInt teamJul 5, 20266 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 teamJul 1, 202610 min read

Query Patterns7 min read

Find Duplicate Rows in SQL: 5 Proven Ways

Five proven ways to find duplicate rows in SQL — GROUP BY, self joins, window functions, EXISTS, and COUNT() OVER — plus how to safely delete duplicates and prevent them.

SqlInt teamJul 2, 20267 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.