Database Notes

Normalisation in DBMS

Normalisation organises tables to remove redundancy and update anomalies, one normal form at a time.

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.

SQL

Users, Roles, GRANT, REVOKE and Least Privilege

Controlling who can do what: creating users, granting the minimum needed, grouping privileges into roles, and the accounts a typical application actua...

SQL

SQL Injection and Parameterised Queries

Why string concatenation lets user input rewrite your query, and why prepared statements make it structurally impossible - with the cases parameters c...

SQL

ACID Properties Explained

Atomicity, consistency, isolation and durability - what each guarantee actually promises, how the database delivers it, and where each one can be weak...

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

First, Second and Third Normal Form

Normalisation worked through on one table: remove repeating groups, then partial dependencies, then transitive ones - with the SQL at each step.

SQL

What NULL Really Means

NULL is not zero, not an empty string and not equal to itself. Learn what it represents, how it spreads through expressions and how to handle it delib...

SQL

What is SQL: Databases, DBMS and RDBMS

SQL is the declarative language used to define and query relational data. Start here to see what a database, a DBMS and an RDBMS actually are.