5 Data
Every entry filed under Data and its subtopics.
What kind of help
Works on
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
- 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
- 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
- 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
- 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
- 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
- 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
- 0238 Redis persistence and high availability: RDB, AOF, replicas and Sentinel Redis keeps data in memory and writes it to disk with RDB snapshots, an append-only file, or both. Replicas copy data to… Intermediate · Explains an idea · Linux Article Administration & persistence 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
- 0201 pg_hba.conf and PostgreSQL authentication methods pg_hba.conf decides who may connect from where and how they must prove who they are. Rules are checked top to bottom and… Intermediate · Explains an idea · Linux Article Install & connect · Security & access 15 Oct 2026
- 0203 Physical backups and point-in-time recovery with pg_basebackup and WAL archiving A base backup plus a continuous archive of WAL files lets you restore a PostgreSQL cluster to any moment after the backup,… Advanced · Explains an idea · Linux Article Backup & restore · Replication & high availability 15 Oct 2026
- 0204 VACUUM, autovacuum and table bloat in PostgreSQL Updates and deletes leave dead row versions behind. VACUUM makes that space reusable, keeps statistics fresh and prevents transaction ID wraparound; autovacuum… Intermediate · Explains an idea · Linux Article Performance & tuning · Roles & administration 15 Oct 2026
- 0216 MySQL vs MariaDB: what actually differs MariaDB started as a fork of MySQL and still speaks the same client protocol, but GTIDs, JSON storage, authentication and tooling have… Intermediate · Explains an idea · Linux Article Choosing a database · MySQL & MariaDB 15 Oct 2026
- 0217 MySQL binary logs and point-in-time recovery The binary log records every change after your last backup. Restore the backup, then replay the binary log up to just before… Advanced · Explains an idea · Linux Article Backup & restore · Replication 15 Oct 2026
- 0221 Oracle Database basics: instance vs database, CDB and PDB An Oracle instance is memory and processes; the database is the files on disk. Since 21c every database is a container database… Beginner · Explains an idea · Linux, Windows Article Concepts & tools 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
- 0068 SQL joins explained: INNER, LEFT and finding rows with no match A join combines rows from two tables using a matching condition. INNER JOIN keeps only matches, LEFT JOIN keeps every row from… Intermediate · Explains an idea · Any system Article Joins 15 Oct 2026
- 0069 NULL in SQL: why = NULL never matches and how to handle missing values NULL means "unknown", so comparisons with it are neither true nor false. Use IS NULL, COALESCE and careful aggregates to avoid rows… Intermediate · Explains an idea · Any system Article Queries 15 Oct 2026
- 0070 Indexes and EXPLAIN: making SQL queries fast An index is a sorted lookup structure that lets the database jump to matching rows instead of reading the whole table. EXPLAIN… Advanced · Explains an idea · Any system Article Indexes & performance 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