How to Pivot Data in SQL: PIVOT vs CASE WHEN
Turn rows into columns in SQL with CASE WHEN or PIVOT. Copy-paste examples for PostgreSQL, SQL Server, Snowflake and DuckDB, plus how to unpivot.
SQL & Local Analytics
Practical SQL for analysts — the patterns you actually reuse, from joins and window functions to running analytics locally with DuckDB.
SQL Interview Questions Analysts Are Actually Asked
The recurring SQL interview patterns behind most data analyst interviews, how to approach each, and how interviewers actually grade the answers.
Text-to-SQL Tools Compared: What Works, What Doesn't
General chat assistants vs BI copilots vs dedicated text-to-SQL products. What each does well, where each breaks, and how to evaluate one.
Why Your SQL Query Is Slow: Reading an Execution Plan
Learn to read EXPLAIN output, spot the difference between a scan and an index, and fix the handful of causes behind most slow SQL queries.
GROUP BY vs HAVING vs WHERE: The Order That Actually Matters
WHERE filters rows, GROUP BY collapses them into groups, HAVING filters the groups. See SQL's real execution order and where each clause belongs.
SQL Joins Explained: Inner, Left, Right and Full
What INNER, LEFT, RIGHT and FULL joins actually do, why rows duplicate or disappear, and how to pick the right one for a report.
Prompting an LLM for SQL You Can Trust
How to get reliable SQL from ChatGPT, Claude or Copilot. What context to give, how to use examples, and the checks that catch wrong joins and made-up columns.
SQL CTE vs Subquery vs Temp Table: Which to Use
CTE, subquery or temp table? A plain-English comparison for analysts, with examples, the performance trade-offs, and a simple rule for choosing.
SQL Date Functions: Fiscal Calendars, Week Starts and Time Zones
Handle dates in SQL without wrong totals. DATE_TRUNC, week starts, fiscal years and time zones explained for analysts, with queries and a calendar table.
How to Find and Fix Duplicate Rows in SQL
Find duplicate rows in SQL with GROUP BY and ROW_NUMBER, then remove them safely. Copy-paste queries, the traps to avoid, and how to stop duplicates coming back.
Cohort Retention Analysis in SQL, Step by Step
Build a cohort retention table in SQL in three steps. Includes a full PostgreSQL query, how to read the triangle, and the mistakes that skew retention.
SQL Cheat Sheet for Data Analysts: 15 Queries You'll Reuse
A practical SQL cheat sheet for data analysts. Fifteen copy-paste queries for filtering, joins, aggregates, CTEs, windows and dates, with plain-English notes.
DuckDB for analysts: local analytics without a warehouse
Query CSV, Parquet and Excel files with plain SQL on your own machine using DuckDB. Practical examples, plus honest limits on concurrency and shared use.
SQL window functions: 10 patterns for real analysis
Window functions keep your rows while you calculate across them. Learn ten patterns: ranking, deduplication, running totals, LAG, cohorts and streaks.