Databases & SQL worksheet with answers

Which keyword sorts the result of a query?

1. ASORT
2. BGROUP BY
3. CARRANGE
4. DORDER BY

Which SQL statement retrieves data from a table?

1. ASELECT
2. BINSERT
3. CUPDATE
4. DCREATE

In a LIKE pattern, what does the % wildcard stand for?

1. AExactly one character in that position of the string
2. BThe end of the string
3. CAny sequence of zero or more characters
4. DAny single digit

Which query returns the number of orders per customer?

1. ASELECT customer_id FROM orders WHERE COUNT(*) > 0
2. BSELECT DISTINCT COUNT(*) FROM orders
3. CSELECT customer_id, COUNT(*) FROM orders ORDER BY customer_id
4. DSELECT customer_id, COUNT(*) FROM orders GROUP BY customer_id

What does a common table expression (WITH name AS (...)) provide?

1. AA new database user
2. BA named temporary result that can be used within one statement
3. CAn index on a column
4. DA permanent table that stays stored on disk until it is dropped

A foreign key is declared with ON DELETE CASCADE. What happens when a parent row is deleted?

1. AThe foreign key in the child rows is set to NULL automatically
2. BThe child rows that reference it are deleted automatically
3. CThe delete is always rejected
4. DThe parent row is copied to an archive table

Why is NATURAL JOIN considered risky in production queries?

1. AIt always returns a Cartesian product
2. BIt joins on every column with the same name, so a new column can silently change the result
3. CIt ignores primary and foreign keys and keeps only NULL rows
4. DIt is not supported by any database

Scores are 90, 90 and 80. Which values does RANK() OVER (ORDER BY score DESC) give?

1. A1, 2, 3
2. B1, 1, 2
3. C1, 1, 3
4. D2, 2, 3