Data and Analytics SQL and Database Fundamentals

Question 1

Which SQL clause is used to filter rows after aggregation?

Accepted Answer

HAVING

Answer

HAVING filters groups created by GROUP BY, whereas WHERE filters individual rows before aggregation.

Question 2

What does a PRIMARY KEY constraint enforce in a relational database?

Accepted Answer

Unique, non-null values per row

Answer

A PRIMARY KEY ensures every row has a unique, non-null identifier in that column or set of columns.

Question 3

Which SQL JOIN returns only rows where there is a match in both tables?

Accepted Answer

INNER JOIN

Answer

INNER JOIN returns only the rows that have matching values in both joined tables.

Question 4

What is the purpose of an index in a relational database?

Accepted Answer

To speed up data retrieval queries

Answer

An index creates a data structure that allows the database engine to find rows faster without scanning the entire table.

Question 5

Which normal form eliminates transitive dependencies?

Accepted Answer

3NF

Answer

Third Normal Form (3NF) removes transitive dependencies, ensuring non-key columns depend only on the primary key.

Data and Analytics Practice Test