Database Modelling, Querying and Programming
Designing a data model and using database operations to store, retrieve, update and protect related data consistently.
How to study A-level Computer Science
Define the problem and representation, trace the state change, justify the algorithm or architecture, then test the result against requirements, evidence and constraints.
Core concepts
Concept 1
A data model defines entities, attributes, relationships, identifiers and constraints for the problem domain.
Exam cue: Derive entities and relationships from requirements before drawing a schema.
Concept 2
Relational design uses keys, tables and normalisation to reduce inappropriate redundancy and update anomalies.
Exam cue: Trace functional dependencies and anomalies when justifying normalisation.
Concept 3
Database programming expresses selection, projection, joins, aggregation and controlled modification while preserving integrity.
Exam cue: State how a query combines tables, filters rows and selects or aggregates fields.
Risk pitfalls and guardrails
Using a non-unique descriptive field as a primary key.
Guardrail: Do not substitute a memorised definition or generic advantage until you have identified the input, state, stakeholder and constraint in the task.
Normalising mechanically without checking the required dependencies.
Guardrail: Do not substitute a memorised definition or generic advantage until you have identified the input, state, stakeholder and constraint in the task.
Building a query by concatenating untrusted input.
Guardrail: Do not substitute a memorised definition or generic advantage until you have identified the input, state, stakeholder and constraint in the task.
Memory anchors
Primary Key
A primary key uniquely identifies each row in a relation.
Foreign Key
A foreign key references a candidate key in another or the same relation.
Normalisation
Normalisation restructures relations to reduce dependency-driven redundancy and anomalies.
Join
A join combines related rows according to a condition.
Transaction
A transaction groups database operations into one controlled unit of work.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A relation needs one attribute that distinguishes every stored student row. Which description gives the primary key's purpose?
An `Order` row stores a `customerId` that links to `Customer`. Which description correctly identifies this foreign key?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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