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IB Computer Science: A3 · Databases

Relational databases, SQL, normalisation. 2 subtopics, 9 key terms.

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In this topic: A3.1 · A3.2

A3.1Relational databases

Table (relation): A set of records with the same fields.
Primary key: A field (or fields) that uniquely identifies each record.
Foreign key: A field linking to the primary key of another table.
Normalization: Organizing tables to reduce redundancy and avoid update anomalies.
Transaction: A unit of work that must be completed fully or not at all.

Relationships: one-to-one, one-to-many (most common), many-to-many (resolved with a link table).

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: 'The key, the whole key and nothing but the key' is a quick way to remember 1NF–3NF.

SELECT: Retrieves data from one or more tables.
WHERE: Filters rows using a condition.
JOIN: Combines rows from tables using matching keys.
Aggregate function: COUNT, SUM, AVG, MIN, MAX: calculate a value from many rows.

GROUP BY groups rows before aggregation; HAVING filters groups (WHERE filters rows).

The full notes, worked example and check questions for this subtopic are in the app.

Exam tip: Read the question for every condition, then check each one appears in your WHERE clause.