Programming

SQL SELECT and WHERE

Start with selecting columns, filtering rows, and sorting a small sample dataset.

Continue with SQL joins.

SQL NULL handling

Understand NULL checks and right-side filters with the shared customers-and-orders data.

Continue from SQL joins.

SQL INNER JOIN vs LEFT JOIN

Compare join results using sample customers and orders data.

Related tool: SQL formatter.

SQL GROUP BY and aggregates

Summarize sample orders with COUNT and SUM, and filter groups using HAVING.

Continue from SQL NULL handling.

SQL constraints

Protect sample customer and order data with keys, required values, and validation rules.

Continue the SQL path after aggregation.

SQL transactions

Commit related changes together or roll back uncommitted changes using the sample data.

Continue after SQL constraints.

SQL indexes

Use indexes for common lookups, inspect a query plan, and weigh storage and write costs.

Continue after SQL transactions.

MySQL and PostgreSQL CONCAT

Compare CONCAT NULL behavior, with MySQL verified locally and PostgreSQL runtime testing still outstanding.

Read the database/version testing note before reusing the examples.

Laravel request lifecycle

Trace a page through routing, middleware, a controller, and a rendered Blade response.

Common JSON syntax errors

Identify common syntax problems and distinguish parsing from application validation.

Related tool: JSON formatter.

URL component encoder and decoder

Encode or decode one component in your browser and learn where component encoding applies.