[Solved] You have these tables:CREATE TABLE Account (AccountID INT PRIMARY KEY, Balance DECIMAL);CREATE TABLE AccountDetails (AccountID INT, Branch VARCHAR(50), FOREIGN KEY (AccountID) REFERENCES... | SQL

SQL - Table Relationships

You have these tables:
CREATE TABLE Account (AccountID INT PRIMARY KEY, Balance DECIMAL);
CREATE TABLE AccountDetails (AccountID INT, Branch VARCHAR(50), FOREIGN KEY (AccountID) REFERENCES Account(AccountID));
Why might this design cause problems enforcing a one-to-one relationship?

AAccount.AccountID is not UNIQUE

BAccountDetails.AccountID is not UNIQUE or PRIMARY KEY, allowing multiple rows per account

CForeign key is missing in AccountDetails

DBalance column should be in AccountDetails

Step-by-Step Solution

Solution:

Step 1: Check constraints on AccountDetails.AccountID
AccountDetails.AccountID is only a foreign key, not UNIQUE or PRIMARY KEY, so multiple rows can exist.
Step 2: Understand one-to-one enforcement
To enforce one-to-one, AccountDetails.AccountID must be UNIQUE or PRIMARY KEY to prevent duplicates.
Final Answer:
AccountDetails.AccountID is not UNIQUE or PRIMARY KEY, allowing multiple rows per account -> Option B
Quick Check:
One-to-one requires UNIQUE or PK on foreign key [OK]

Quick Trick: Foreign key must be UNIQUE or PK for one-to-one [OK]

Common Mistakes:

MISTAKES

Assuming foreign key alone enforces one-to-one
Confusing missing foreign key with missing uniqueness
Thinking Balance column placement affects relationship

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You have these tables:

Step 1: Check constraints on AccountDetails.AccountID

Step 2: Understand one-to-one enforcement

Final Answer:

Quick Check:

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