Analytics2026-07-21
SQL Query for Month-over-Month Growth Rate (MySQL & PostgreSQL)
Write a SQL query to calculate month-over-month growth rate using window functions. Includes LAG(), CTE approach, and handling NULL months.
SQL Guides & Tutorials
Practical SQL examples, query patterns, and tips for data analysts and developers.
Fundamentals2026-07-19
How to JOIN Three Tables in SQL: Real-World Example with Explanation
Step-by-step guide to joining 3+ tables in SQL. Covers INNER JOIN, LEFT JOIN ordering, and common mistakes that cause duplicate rows.
Window Functions2026-07-17
Calculate a Running Total in SQL: Window Function vs Self-Join
Two approaches to cumulative sums in SQL — the modern SUM() OVER() window function and the legacy self-join. With MySQL, PostgreSQL, and BigQuery examples.
Data Cleaning2026-07-14
Find and Delete Duplicate Rows in SQL (Without Deleting Originals)
How to identify duplicates with GROUP BY HAVING, and safely delete them using ROW_NUMBER() or a CTE. Works in MySQL, PostgreSQL, and SQL Server.
Guides2026-07-11
Natural Language to SQL: How AI Converts English to Database Queries
How text-to-SQL tools work under the hood — prompt engineering, schema awareness, and accuracy benchmarks. Plus when AI-generated SQL needs human review.
Common Queries2026-07-26
SQL: Select the Latest Record Per Group (3 Methods Compared)
Get the most recent row for each group in SQL. Compares ROW_NUMBER(), correlated subquery, and DISTINCT ON approaches across MySQL, PostgreSQL, and BigQuery.
Aggregation2026-07-26
SQL COUNT with Conditions: Conditional Aggregation Explained
Count rows that meet specific conditions using CASE WHEN, FILTER, and IF. Includes counting distinct values with conditions and pivot-style summaries.
Data Manipulation2026-07-26
SQL UPDATE from Another Table: JOIN-Based Updates Explained
Update a table using values from another table. Covers MySQL, PostgreSQL, and SQL Server syntax differences with real examples.
Fundamentals2026-08-18
SQL Date Filtering: WHERE, BETWEEN & DATE Functions Explained with Examples
Filtering by date is where beginners and pros diverge. Learn the exact WHERE clauses for today, yesterday, last 7 days, and current month across MySQL, PostgreSQL, and SQL Server.
Guides2026-08-18
SQL CTE vs Subquery: When to Use Which (Performance Tested)
CTEs and subqueries often produce identical results — but not identical plans. Here's when a WITH clause actually helps, when it hurts, and how to test it on your own database.
Data Manipulation2026-08-18
How to Pivot Data in SQL: Rows to Columns Without a Pivot Function
Turn category rows into columns with conditional aggregation — the portable technique that works on MySQL, PostgreSQL, SQLite, and SQL Server. Includes dynamic pivots.
Fundamentals2026-08-19
SQL Window Functions for Beginners: ROW_NUMBER, RANK, LAG & Running Totals
Window functions are the most powerful SQL feature beginners skip. This guide explains OVER(), PARTITION BY, and ORDER BY with practical examples — row numbering, rankings, moving averages, and differences from GROUP BY.
Advanced2026-08-20
Recursive CTE in SQL: 5 Real-World Examples (Employee Trees, Date Series, Graph Paths)
Recursive CTEs explained with five practical examples: org charts, bill-of-materials, date range expansion, Fibonacci, and graph traversal. Includes the anchor/recursive structure and infinite-loop safeguards.
Performance2026-08-21
SQL Indexing for Slow Queries: The Practical Guide (With EXPLAIN Examples)
Why your SQL is slow and how indexes fix it: the index fundamentals, when indexes hurt, how to read EXPLAIN output, and the exact index designs for the most common slow-query patterns.
Analytics2026-08-28
SQL Year-over-Year Growth: Compare This Year vs Last Year (with CTEs)
Write SQL to compare this year vs last year by month: YoY growth rate with LAG(), handling missing periods, and a ready-to-adapt CTE template.
Functions2026-08-28
SQL String Aggregation: GROUP_CONCAT, STRING_AGG & LISTAGG Compared
Concatenate multiple rows into one string in SQL: MySQL GROUP_CONCAT, PostgreSQL STRING_AGG, SQL Server STRING_AGG, Oracle LISTAGG — with separators and ordering.
Fundamentals2026-08-28
SQL: Find Rows with the Max Value per Group (3 Clean Solutions)
Get the full row that contains the max value per group in SQL: ROW_NUMBER() window function, NOT EXISTS, and a self-join — with MySQL and PostgreSQL examples.
Analytics2026-09-04
SQL: Group Data Into Time Buckets (15-Min, Hourly, Daily) — MySQL & PostgreSQL
Group timestamps into 15-minute, hourly, or daily buckets for reporting. Covers DATE_FORMAT, DATE_TRUNC, UNIX timestamp math, and the BigQuery TIMESTAMP_TRUNC approach with examples.
Common Queries2026-09-04
SQL: Find Consecutive Days / Streaks (Login Streaks, Habit Tracking)
Write a SQL query that finds consecutive-day streaks — like days-in-a-row logins or habits. Covers the date-minus-row_number gap-and-islands technique with MySQL, PostgreSQL, and BigQuery examples.
Common Queries2026-09-04
SQL: Find Differences Between Two Tables (3 Methods Compared)
Compare two tables and find rows that differ — missing rows, extra rows, and changed values. Covers EXCEPT, NOT EXISTS, and FULL OUTER JOIN with MySQL, PostgreSQL, and BigQuery syntax.