Assume that the "employee" table has already been created. Which of the following SQL statements correctly creates a "project" table with constraints referencing the "employee" table?
a) CREATE TABLE project (
project_id INT PRIMARY KEY,
project_name VARCHAR(100) NOT NULL,
employee_id INT,
FOREIGN KEY (employee_id) REFERENCES employee(employee_id));
b) CREATE TABLE project (
project_id INT PRIMARY KEY,
project_name VARCHAR(100) NOT NULL,
employee_id INT,
CONSTRAINT fk_employee FOREIGN KEY (employee_id) REFERENCES employee(employee_id) ON DELETE CASCADE);
c) CREATE TABLE project (
project_id INT PRIMARY KEY,
project_name VARCHAR(100) NOT NULL,
employee_id INT NOT NULL,
CHECK (employee_id IN (SELECT employee_id FROM employee)),
FOREIGN KEY (employee_id) REFERENCES employee(employee_id));
d) CREATE TABLE project (
project_id INT PRIMARY KEY,
project_name VARCHAR(100) NOT NULL,
employee_id INT,
CONSTRAINT FOREIGN KEY (employee_id) REFERENCES employee(employee_id));
