Databases & SQL worksheet with answers

Which SQL statement retrieves data from a table?

1. ACREATE
2. BINSERT
3. CSELECT
4. DUPDATE

Which statement deletes a whole table, including its structure?

1. ATRUNCATE ROWS
2. BDELETE FROM
3. CREMOVE TABLE
4. DDROP TABLE

What does NULL represent in SQL?

1. AThe number zero in numeric columns
2. BA missing or unknown value
3. CA false Boolean
4. DAn empty string

What does GRANT SELECT ON employees TO alice do?

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

The orders table has 5 rows, each referring to an existing customer. The customers table has 3 rows. How many rows does an INNER JOIN on customer_id return?

1. A8
2. B3
3. C5
4. D15

A table stores the customer's address on every order row. Changing the address in one row but not in the others is an example of:

1. AAn update anomaly
2. BA deletion anomaly
3. CA phantom read
4. DAn insertion anomaly

Two-phase locking (2PL) ensures:

1. AConflict-serializable schedules
2. BThat deadlocks can never happen
3. CThat no locks are needed
4. DThat transactions never wait

What does the following return: SELECT name FROM students WHERE grade > (SELECT AVG(grade) FROM students)?

1. AAn error because subqueries are not allowed in WHERE
2. BThe average grade of all students
3. CStudents with a grade above the average grade
4. DStudents with the highest grade only