SQL - Table Relationships
Which SQL constraint is commonly used to enforce a one-to-one relationship between two tables?
Which SQL constraint is commonly used to enforce a one-to-one relationship between two tables?
easy📝 Syntax Q12 of 15
Step-by-Step Solution
Solution:
Step 1: Identify constraint enforcing uniqueness
To ensure one-to-one, the foreign key must be unique so no duplicates link to the same row.Step 2: Match constraints to this need
UNIQUE constraint on the foreign key column enforces this, while FOREIGN KEY alone does not guarantee uniqueness.Final Answer:
UNIQUE constraint on the foreign key column -> Option CQuick Check:
Unique foreign key = one-to-one [OK]
Quick Trick: Use UNIQUE on foreign key to enforce one-to-one [OK]
Common Mistakes:
MISTAKES- Using FOREIGN KEY without UNIQUE allows many-to-one
- Confusing CHECK with uniqueness
- Assuming NOT NULL enforces one-to-one
Master "Table Relationships" in SQL
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