You want to split user data into two tables: User and UserProfile. Each user has exactly one profile. Which design best enforces this one-to-one relationship?
hard📝 Application Q15 of 15
SQL - Table Relationships
You want to split user data into two tables: User and UserProfile. Each user has exactly one profile. Which design best enforces this one-to-one relationship?
AUser and UserProfile share the same primary key column
BUserProfile has a foreign key to User without UNIQUE constraint
CUserProfile has no foreign key but a separate primary key
DUserProfile has a foreign key to User with UNIQUE constraint on that foreign key
Step-by-Step Solution
Solution:
Step 1: Understand one-to-one enforcement methods
One way is to share the same primary key in both tables, ensuring exactly one matching row.
Step 2: Compare options
User and UserProfile share the same primary key column uses the same primary key in both tables, which is a strong one-to-one design. UserProfile has a foreign key to User with UNIQUE constraint on that foreign key is valid but less strict. Options B and C do not enforce one-to-one properly.
Final Answer:
User and UserProfile share the same primary key column -> Option A
Quick Check:
Shared primary key = strict one-to-one [OK]
Quick Trick:Use shared primary key for strict one-to-one [OK]
Common Mistakes:
MISTAKES
Ignoring uniqueness on foreign key
Assuming foreign key alone enforces one-to-one
Not linking tables properly
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