Databases, SQL & normalization

Relational basics

• Data lives in tables (relations) made of rows (records) and columns (fields).
• A primary key uniquely identifies a row; a foreign key references another table's primary key, linking the two.

Normalization

• 1NF: atomic values only — no repeating groups or lists in a cell.
• 2NF: 1NF and no non-key column depends on only *part* of a composite key.
• 3NF: 2NF and no *transitive* dependency (non-key column depending on another non-key column).

ACID (transaction guarantees)

• Atomicity — all steps happen, or none do.
• Consistency — a transaction moves the DB from one valid state to another.
• Isolation — concurrent transactions don't corrupt each other.
• Durability — once committed, data survives a crash.

Core SQL

SELECT name, score
FROM   results
WHERE  score >= 60
ORDER BY score DESC;