SQL
PostgreSQL, MySQL, SQL Server, Oracle and SQLite Compared
One reference table for the differences that actually break code: paging, auto increment, strings, dates, upserts and the features each product lacks.
#Intermediate
Material for readers past the basics.
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HTML
The Console and the Network Panel
The Console reports what went wrong. The Network panel shows what was requested, in what order, and how big it was. Between them they explain most pag...
HTML
The Elements Panel
The Elements panel shows the live DOM, not your file. That difference is why it is the first place to look when markup behaves in a way the source doe...
HTML
Core Web Vitals and Mobile Friendliness
Three measurements taken from real visits, and one indexing rule that decides which version of your page Google actually reads.
SQL
What Indexes Are and Why They Exist
An index is a sorted lookup structure the database maintains for you. Learn how a B-tree finds a row, what an index costs, and the clustered index in...
SQL
BEGIN, COMMIT, ROLLBACK and Savepoints
Grouping statements into one unit of work that either fully applies or fully undoes. Learn transaction boundaries, savepoints, autocommit and what sil...
SQL
Temporary Tables vs CTEs vs Views vs Derived Tables
Four ways to name an intermediate result, and a decision rule for choosing between them based on scope, reuse and whether you need an index.
SQL
Temporary Tables and Session Scope
A real table that exists only for your session. Learn CREATE TEMPORARY TABLE, its scope and lifetime, indexing it, and the dialect differences.
HTML
Accessible Names and the Accessibility Tree
Every control has a name, a role and a state, and the browser works them out in a fixed order. Knowing that order explains almost every screen reader...
HTML
Selecting and Changing Elements
querySelector, classList, dataset and the methods that actually get used. The small set of DOM operations that covers most day to day work.
HTML
Loading Scripts: defer, async and type=module
Where a script tag sits and which attribute it carries decides whether your page paints in half a second or four. Three loading behaviours, and when e...
SQL
Finding and Removing Duplicates
Detect duplicate rows on any definition of "duplicate", inspect them safely, delete all but one, and add the constraint that stops them coming back.