5 Data
Every entry filed under Data and its subtopics.
What kind of help
What do these mean?
- Beginner
- You are new to this topic.
- Intermediate
- You use it, and want to get better.
- Advanced
- You know it well and need the details.
- Guided project
- Build something small from start to finish, step by step.
- Explains an idea
- Plain words on how something works and why.
- Step by step
- Numbered steps to get one task done.
- Cheat sheet
- Commands and options in a table, to look up fast.
- Fixes an error
- An error message, what it means, and how to solve it.
21 entries match these filters
- 0299 What is YAML? YAML is a human friendly text format for configuration files where indentation shows structure instead of brackets. Beginner · Explains an idea · Any system Article CSV & JSON 15 Oct 2026
- 0293 What is SQL? SQL is the language you use to ask a relational database questions and to add, change or delete its data. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
- 0292 What is a database? A database is an organised store of data that programs can search, update and share safely, even with many users at once. Beginner · Explains an idea · Any system Article Choosing a database 15 Oct 2026
- 0295 What is a transaction? A transaction groups several database changes so they all happen together or not at all, keeping the data consistent. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
- 0296 What is a primary key? A primary key is the column that uniquely identifies each row in a table, like an ID number nobody else can have. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
- 0297 What is a foreign key? A foreign key is a column that points to the primary key of another table, linking related rows together. Beginner · Explains an idea · Any system Article Joins 15 Oct 2026
- 0294 What is an index (database)? A database index is a lookup structure that lets the database find rows fast instead of reading the whole table. Beginner · Explains an idea · Any system Article Indexes & performance 15 Oct 2026
- 0298 What is JSON? JSON is a simple text format for structured data, made of names, values, lists and nested objects, used everywhere on the web. Beginner · Explains an idea · Any system Article CSV & JSON 15 Oct 2026
- 0232 mongosh cheat sheet: CRUD, indexes and explain() The mongosh commands you use every day: switching databases, inserting, querying, updating and deleting documents, creating indexes and checking a query plan… Beginner · Cheat sheet · Any system Article Basics 15 Oct 2026
- 0236 Redis data types and commands: a quick reference Redis stores values under keys, and each value has a type: string, hash, list, set, sorted set or stream. The essential commands… Beginner · Cheat sheet · Any system Article Basics 15 Oct 2026
- 0260 Design and build a library database in SQLite: tables, keys, joins, reports and backups Model books, members and loans, create tables with keys and constraints, load sample data, write join and aggregate reports, add indexes checked… Beginner · Guided project · Any system Article Joins · Queries 15 Oct 2026
- 0241 Choosing a database: relational, document or key-value Relational databases, document stores like MongoDB and key-value stores like Redis each fit different jobs. An honest look at what each does… Beginner · Explains an idea · Any system Article Choosing a database · Database operations 15 Oct 2026
- 0231 MongoDB documents and collections compared with SQL tables MongoDB stores data as JSON-like documents grouped in collections instead of rows in tables. This explains the model, the _id field, embedding… Beginner · Explains an idea · Any system Article Basics · Choosing a database 15 Oct 2026
- 0215 mysql command-line client cheat sheet The connection options, built-in commands and everyday SQL you need in the mysql (and mariadb) command-line client, on one page. Beginner · Cheat sheet · Any system Article Administration · Queries 15 Oct 2026
- 0199 psql meta-commands cheat sheet The backslash commands you use every day in psql: connecting, listing databases, tables and roles, describing objects, timing queries, expanded output and… Beginner · Cheat sheet · Any system Article Install & connect · Roles & administration 15 Oct 2026
- 0077 SQL cheat sheet: a runnable reference for everyday queries One SQL file that builds a tiny database and demonstrates filtering, sorting, grouping, joins, CASE, CTEs, window functions, safe updates and indexes.… Beginner · Cheat sheet · Any system Script Joins · Queries 15 Oct 2026
- 0072 CSV vs JSON: choosing a format and avoiding the classic pitfalls CSV is a simple table of text; JSON holds nested, typed data. Both break in predictable ways: quoting, delimiters, encodings, numbers and… Beginner · Explains an idea · Any system Article CSV & JSON 15 Oct 2026
- 0073 Fix: json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0) Python's json module found nothing it could parse at the very first character. The input is usually empty, HTML, or already consumed.… Beginner · Fixes an error · Any system Article Common errors · CSV & JSON 15 Oct 2026
- 0075 CSV to JSON converter (Python, standard library) Convert any CSV file with a header row into a JSON array or JSON Lines. Handles quoted fields, a byte order mark,… Beginner · Step by step · Any system Script CSV & JSON · Files & automation 15 Oct 2026
- 0067 Your first SQL queries: SELECT, WHERE, ORDER BY, LIMIT and GROUP BY Read data from a table, keep only the rows you want, sort them, take the first few, and summarize groups with COUNT,… Beginner · Step by step · Any system Article Queries 15 Oct 2026
- 0009 CSV to JSON converter A small command-line tool that turns a CSV file into a JSON array of objects, with optional number detection, custom delimiters and… Beginner · Step by step · Any system Script CSV & JSON · Files & automation 15 Oct 2026