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A primary key uniquely identifies each record in a table. Its values must not be duplicated or missing. A person's name is usually unsuitable because different people can share a name. A unique MemberID is more dependable.
Worked example
Two records have Name="Alex Lee" but MemberID values 104 and 105. The keys are unique even though the names match. A key constraint prevents duplicate key values; it does not prove the two records describe different real people.
Validation checks whether input meets a rule, not whether it is true. A presence check can require a name, a range check can limit age, and a format check can check the layout of an identifier. A validly formatted wrong date may still pass.
Independent design
Choose a primary key for a school library's books when several copies share a title. Explain why a separate copy identifier is needed. Choose a validation rule for a publication year and explain one incorrect value that could still pass it.
This course's core database tasks use a single table. Multiple-table relationships and advanced key taxonomy are optional later study.
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Independent Practice: Choose a key
Independent Practice: Choose a key
- Two members can share a name. Is Name guaranteed unique: yes or no? [Space 1]
- Should a primary key allow duplicate values: yes or no? [Space 2]
- Should a primary key be missing: yes or no? [Space 3]
Interactive exercises for Module 2 and beyond require an active plan.