[Solved] Consider this table design:CREATE TABLE Employee ( EmployeeID INT PRIMARY KEY, Name VARCHAR(50) );... | SQL

SQL - Table Relationships

Consider this table design:

CREATE TABLE Employee (
  EmployeeID INT PRIMARY KEY,
  Name VARCHAR(50)
);

CREATE TABLE EmployeeDetails (
  DetailID INT PRIMARY KEY,
  EmployeeID INT,
  Address VARCHAR(100),
  FOREIGN KEY (EmployeeID) REFERENCES Employee(EmployeeID)
);

What is missing to enforce a one-to-one relationship between Employee and EmployeeDetails?

AAdd PRIMARY KEY on EmployeeID in EmployeeDetails

BAdd NOT NULL constraint on EmployeeID in EmployeeDetails

CRemove FOREIGN KEY constraint

DAdd UNIQUE constraint on EmployeeID in EmployeeDetails

Step-by-Step Solution

Solution:

Step 1: Identify current constraints
EmployeeDetails has a foreign key to Employee but no uniqueness on EmployeeID, so multiple details can link to one employee.
Step 2: Determine what enforces one-to-one
Adding UNIQUE on EmployeeID ensures each employee links to at most one detail, enforcing one-to-one.
Final Answer:
Add UNIQUE constraint on EmployeeID in EmployeeDetails -> Option D
Quick Check:
Unique foreign key needed for one-to-one [OK]

Quick Trick: Add UNIQUE on foreign key column for one-to-one [OK]

Common Mistakes:

MISTAKES

Assuming NOT NULL enforces one-to-one
Removing foreign key breaks relationship
Confusing primary key with foreign key uniqueness

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Consider this table design:

Step 1: Identify current constraints

Step 2: Determine what enforces one-to-one

Final Answer:

Quick Check:

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