DA0-002 Data Concepts and Environments Practice Question
A university database stores student information in a normalized schema. The 'students' table has a primary key 'student_id'. The 'enrollments' table has a foreign key 'student_id' referencing 'students'. Which two of the following are true about primary and foreign keys? (Select TWO)
⚠ Common exam trap
Many candidates assume a foreign key can reference any column, forgetting that the referenced column must have a unique constraint (primary key or unique) to ensure a single target row, which is a common point of confusion in DA0-001.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A foreign key ensures referential integrity between tables
A foreign key enforces referential integrity by ensuring that every value in the foreign key column of the 'enrollments' table matches a valid primary key value in the 'students' table. This prevents orphaned records and maintains consistency across related tables in a normalized relational database.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A foreign key must have the same name as the primary key it references
Why it's wrong here
Foreign keys can have different names.
- ✓
A foreign key ensures referential integrity between tables
Why this is correct
Foreign keys enforce that values match the referenced primary key.
- ✗
A foreign key can reference a column that is not a primary key
Why it's wrong here
Foreign keys typically reference a primary key or unique constraint.
- ✗
A table can have multiple primary keys
Why it's wrong here
A table can have only one primary key, but it can be composite.
- ✓
A primary key column cannot contain NULL values
Why this is correct
Primary keys enforce uniqueness and non-nullability.
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