Databases & SQL is a core part of A-Level Computer Science. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
DatabaseAn organised, persistent store of data.
Tables, records & fieldsRows are records; columns are fields.
Primary keyA field that uniquely identifies each record.
SQLLanguage to query and manage a relational database.
Relational databaseLinked tables connected by keys.
QueryA request to select or change data.
1NFAtomic values only — no repeating groups or lists in a cell.
2NF1NF plus no partial dependencies on a composite key.
3NF2NF plus no transitive dependencies — non-key attributes depend only on the key.
Functional DependencyWhen one attribute determines another.
Transitive DependencyA non-key attribute depending on another non-key attribute.
AnomalyAn update, insert or delete problem caused by redundant data.
SELECTSQL clause choosing which columns to return.
WHERESQL clause filtering rows before grouping.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What is the purpose of database normalisation?✗ To make the database run faster. ✓ To reduce redundancy and avoid update anomalies.
What does an INNER JOIN return?✗ All rows from both tables combined. ✓ Only rows with matching values in both tables.
Is the DBMS the same thing as the database?✗ Yes - DBMS is simply the technical name for the data itself. ✓ No - the database is the organised collection of data; the DBMS is the software layer that manages access to it, like MySQL or Oracle.
Can you safely delete a customer record while orders still reference it?✗ Yes - deleting a parent record has no effect on other tables. ✓ No - referential integrity forbids leaving orphaned foreign keys; the DBMS will block the deletion or cascade it according to defined rules.
Is data redundancy good because it acts as a backup?✗ Yes - storing each fact several times protects against data loss. ✓ No - uncontrolled duplication inside a database causes inconsistencies when copies diverge; backups are deliberate, separate, managed copies of the whole database.
Practise Databases & SQL — free games
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