Oracle PL/SQL and SQL Online Test

Consider the following code:

CREATE OR REPLACE FUNCTION count_users 
RETURN NUMBER 
IS 
  user_count NUMBER;
BEGIN
  SELECT COUNT(*) INTO user_count FROM users;
  RETURN user_count;
END;
/

Select the statements that are correct.

(multiple correct answers possible)

Consider the following table definition:

CREATE TABLE couples(
  id NUMBER PRIMARY KEY NOT NULL,
  first_name VARCHAR2(50) NOT NULL,
  last_name VARCHAR2(50) NOT NULL
);

Later the following code is executed:

DECLARE
  husband_id NUMBER;
BEGIN
  SELECT id INTO husband_id FROM couples WHERE first_name = 'John' AND last_name = 'Johnson';
  INSERT INTO couples(id, first_name, last_name) VALUES(husband_id + 1, 'Jane', 'Johnson');
END;

Select the exceptions that might be raised.

(multiple correct answers possible)

Given the following data definition, write a query that returns the number of students whose first name is John.

TABLE students
   id INTEGER PRIMARY KEY,
   firstName VARCHAR(30) NOT NULL,
   lastName VARCHAR(30) NOT NULL