Two-Table Databases and SQL
Implement two linked tables with referential integrity and read, explain and write required National 5 SQL operations.
How to study National 5 Computing Science
Move from functional requirements to designs and implementation, trace data and code carefully, and support testing and evaluation with evidence.
Core concepts
Concept 1
A relational solution at this level uses two linked tables and enforces referential integrity.
Exam cue: Trace FROM and join conditions before applying WHERE filters and ORDER BY.
Concept 2
SELECT, FROM and WHERE can use AND, OR, less than, greater than and equality; ORDER BY can sort on at most two fields.
Exam cue: Use a precise WHERE condition for UPDATE or DELETE so only intended records change.
Concept 3
INSERT adds, UPDATE changes and DELETE removes records; an equi-join matches equal key values across the two tables.
Risk pitfalls and guardrails
Omitting the join condition and producing every possible pair of rows.
Guardrail: Check option route, data type, valid boundary, loop condition, array index, identifier and expected output before committing to the response.
Confusing INSERT, UPDATE and DELETE.
Guardrail: Check option route, data type, valid boundary, loop condition, array index, identifier and expected output before committing to the response.
Using SQL features beyond the specified National 5 range as assumed requirements.
Guardrail: Check option route, data type, valid boundary, loop condition, array index, identifier and expected output before committing to the response.
Memory anchors
Referential integrity
Every foreign-key value must match an existing related primary-key value.
SELECT and FROM
Choose the output fields, then identify the table or tables supplying them.
WHERE
Filter records using the required comparisons joined by AND or OR.
ORDER BY
Sort query output by one or at most two stated fields.
Data changes
INSERT adds a record, UPDATE changes records and DELETE removes records.
Equi-join
Match a foreign key to its related primary key using equality.
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
For the same query, which sort order gives A to Z?
A query needs class then surname ordering. What design should record?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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