Databases & SQL worksheet with answers

What does WHERE country IN ('NL', 'BE', 'DE') do?

1. AKeeps rows whose country value contains all three codes at once
2. BKeeps rows whose country equals any value in the list
3. CKeeps rows whose country is not in the list
4. DSorts rows in the order of the list

What is a surrogate key?

1. AAn artificial identifier with no business meaning, such as an auto-increment id
2. BA key made from real-world data such as an email address
3. CA key that refers to another table
4. DA key that is only used in views

Which SQL statement adds new rows to a table?

1. AINSERT
2. BALTER
3. CUPDATE
4. DSELECT

In relational algebra, the selection operator (σ) corresponds to which SQL clause?

1. AORDER BY
2. BSELECT list
3. CWHERE
4. DGROUP BY

What does the functional dependency A → B mean?

1. AEach value of A is associated with exactly one value of B
2. BA and B are both primary keys
3. CEach value of B is associated with exactly one value of A
4. DA is a foreign key referencing B

What does GRANT SELECT ON employees TO alice do?

1. AAllows the user alice to read the employees table
2. BAllows alice to update and delete rows in the employees table
3. CMakes alice the owner of the database
4. DCopies the employees table to alice

Table employee(emp_id, dept_id, dept_name) has the key emp_id, and dept_id → dept_name. Which statement is correct?

1. AIt is in 2NF but not in 3NF
2. BIt is not in 2NF
3. CIt is not in 1NF
4. DIt is in BCNF and therefore in 3NF

After customers LEFT JOIN orders, why use COUNT(o.id) rather than COUNT(*) to count orders per customer?

1. ACOUNT(o.id) counts only distinct customers
2. BCOUNT(*) counts the NULL-filled row as 1 for customers without orders
3. CCOUNT(*) is not allowed after a join
4. DCOUNT(*) ignores rows with NULL values