CS Database Management & SQL 2

Question 1

Which SQL clause is used to filter groups after aggregation with GROUP BY?

Accepted Answer

HAVING

Answer

HAVING filters aggregated groups, while WHERE filters rows before grouping.

Question 2

A table's primary key must be:

Accepted Answer

Unique and not null

Answer

A primary key uniquely identifies each row and cannot contain NULL values.

Question 3

Which JOIN returns all rows from the left table plus matching rows from the right table?

Accepted Answer

LEFT OUTER JOIN

Answer

A LEFT OUTER JOIN keeps every left-table row, filling unmatched right-side columns with NULL.

Question 4

What does the SQL statement 'DELETE FROM orders;' do without a WHERE clause?

Accepted Answer

Removes all rows from the orders table

Answer

DELETE without WHERE removes every row but leaves the table definition intact, unlike DROP TABLE.

Question 5

A relation is in second normal form (2NF) when it is in 1NF and:

Accepted Answer

No non-key attribute depends on only part of a composite key

Answer

2NF eliminates partial dependencies of non-key attributes on a composite primary key.

(CS) Computer Science Practice Test