Window Functions, Joins, CTEs and Subqueries
Once you've got filtering and grouping down, SQL starts asking harder questions. Which doctor handles the most visits? Which department has the most…
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PostgreSQL Constraint Naming Convention: Which Pattern to Use, and How to Find the Names That Drifted
Disclosure: I build Schemity , a desktop ERD tool - this post is from our blog and uses it for the examples. TL;DR: Use the pattern PostgreSQL alrea…
A Practical Guide to SQL Joins, Subqueries, CTEs, and Window Functions.
A hospital database rarely stores every useful detail in one table. Patient details may be stored separately from visit records. Doctor, department,…
Exploring Hospital Data: Window Functions, Joins, CTEs and Subqueries
Introduction While working on my hospital dataset, I realised that SQL is not just about retrieving data. It can also help me compare hospital visit…
CreatorDesk: a self-hosted approval loop for commission artists
This is a submission for the Hacktoberfest Open-Source AI Challenge Week 2: Side Hustle What I Built CreatorDesk is a self-hosted, open-source tool…
Logging in PL/SQL that survives ROLLBACK (and 4 mistakes to avoid)
You get a call: last night's batch failed, the transaction rolled back, and now someone asks "what happened?" You open your log table. It's empty. I…
Joins In PostgreSQL
Joins are one of those topics where everyone nods along when you explain them, then freezes up the moment they have to write one on the spot, in fro…
Reading the CVSS 9.8 score of CVE-2026-108474 without overreading it
Reading the CVSS 9.8 score of CVE-2026-108474 without overreading it Vulnerability overview CVE-2026-108474 carries a CVSS v3 score of 9.8 and is cl…
PostgreSQL EXPLAIN ANALYZE: What I Actually Look At in Query Plans
PostgreSQL EXPLAIN ANALYZE: What I Actually Look At in Query Plans Every slow query I have ever chased started the same way: someone guessing. "Prob…
One Null in the Subquery and Your NOT IN Returned Nothing
Marketing wanted a list. Every customer who had never placed an order. The query was short and read like English. Select from customers where id is…
Modelling Medical Device Size Variants as SKUs: A Ureteral Stent Example
Medical device catalogues have a recurring design problem: one product, many size variants. A ureteral stent might come in six diameters, a dozen le…
PCAD-31-02 in Code: Validation Checks and Safe sqlite3 Queries Behind 30 of the 48 Items
The Python Institute PCAD-31-02 exam has 48 items, and 30 of them come from two syllabus blocks: Data Acquisition and Pre-Processing (14) and Progra…
Announcing det: - Fast, local-first SQL ETL workspace and pipeline orchestration engine
What if you could build complete, production-grade ETL pipelines in Pure SQL… without Jinja templates, without a database server, and without heavy…
5 SQL window-function traps that show up in data engineering interviews (with runnable DuckDB examples)
Window functions are the most common SQL topic in data engineering interviews, and most candidates know the syntax. The follow-up questions are wher…
WHERE vs HAVING in SQL: A Simple Way to Understand the Difference
If you’ve ever mixed up WHERE and HAVING, you’re not alone. They both filter data, so it feels like you should be able to use either one. But they f…
Merging Two Messy CSVs: The Key Problems Excel Formulas Hide From You
Merging Two Messy CSVs: The Key Problems Excel Formulas Hide From You You have two spreadsheets. One is your export, one is the client's. Someone sa…
Why Your Database Gets Slower as Your App Grows
Hello, I’m Arthur. One problem developers often face is that an application works perfectly when it has a few hundred records, but starts slowing do…
Start and End Dates of the Longest Rising Period
Problem Description The stock table records the daily closing prices of many stocks, with the fields CODE (stock code), DT (trading date) and CL (cl…
Fix It in the Model or Fix It in the Source?
Fix It in the Model or Fix It in the Source? The first compile error in a converted CA 2E program forces a decision most teams never make on purpose…
Stored Procedures
Stored Procedures A deep-dive walkthrough of stored procedures — covering parameters and output parameters, plan caching and recompilation specific…
Postgres Let Two Rows Through a Unique Index: The glibc Collation Trap After an OS Upgrade
If a unique index suddenly tolerates duplicates, or WHERE email = ... misses a row that a sequential scan finds, the index is sorted by collation ru…
Three months of sales vanished, and every dbt run was green
In this article I'll show you how a dbt incremental model that looked perfectly reasonable wiped out three months of finance data, why none of our c…
The Empty SMALLINT Column That Led Me to Nine More Missing Types
I had written a stock market analysis program before. One of its tables had a SMALLINT column. When I tested LogCarver against that table, every row…
SqlJam: Move Tables Across Databases with Schema, Data and All
Tables, indexes, constraints, sequences, partitions and rows, in one go. 1. Overview SqlJam : Move tables across databases. Schema, data and all. A…
How AI can investigate a 12 GB export without reading it into a prompt
Imagine asking an AI assistant for the average order value in a 12 GB sales export. It finds an amount column and suggests AVG(line_amount) . The qu…
I gave my text-to-SQL agent a business glossary. One version helped a lot, one did nothing.
A text-to-SQL agent sees table and column names. It does not know that "revenue" in your company means billing_invoice.total_net , only for invoices…
Database Indexes, Explained Like a Book Index
Imagine a table with ten million users. You need one person, and all you have is an email address. Without a useful index, the database may have to…
My Journey into Data Analytics
Data is everywhere — but turning data into meaningful insights is a skill I’m excited to build. As an AI & Data Science student, I’m exploring t…
Build a Knowledge Layer for SQL Agents with OKF (Part 2)
You connect an AI agent to your shop's database and ask a simple question: "How many active customers do we have?" The agent looks at the tables: cu…
Replacing deep OFFSET pagination in D1: rows read and inserts between pages
LIMIT 20 OFFSET ... makes the next page of a list easy to express. But deeper pages require skipping more rows without returning them. Using an inde…